This month’s Mystery Box Ingredient was white chocolate. “Well,” I thought, “surely I can make something with that.” And then I thought “stop calling yourself Shirley.” (Fun fact – I have a bowling shirt with the name Shirley embroidered on it. Just ‘cuz.)
One of my favorite combos is white chocolate and lime because the even and unassuming flavor of the white chocolate really evens out the tartness of the lime. I racked my brain and scoured my baking books until I came up with a totally fabu way to incorporate all this goodness into just one tiny cupcake.
Here’s what I came up with: I made a sour cream cupcake which I flavored with white chocolate, filled it up with a little homemade lime curd, and topped it off with white chocolate buttercream frosting. I know, right? It came out just as I hoped. The cupcakes really carried the flavor of the white chocolate I added, the lime curd was tongue-achingly tart but was balanced out perfectly by the frosting. (Reader poll: have you ever had something so tart and sweet at the same time that your tongue actually started aching? That’s what this cupcake did to me.)
I started off by making the curd the night before I prepared the cupcakes so it would have time to set. I found this recipe on allrecipes.com and another one in The Joy of Cooking, and ended up making a hybrid of the two.
- 1/2 cup sugar
- 1/4 cup (1/2 stick) unsalted butter
- 3/4 cup fresh lime juice (you can use key limes if you like, but I used regular limes – 5 medium ones)
- 1 Tbsp lime zest
- 3 eggs – beaten until they’ve paled in color
Combine your zest with your sugar by rubbing them together with your fingertips. Let that sit while you juice your limes. Once that’s done, combine the lime sugar, butter, and lime juice in the top portion of a double boiler over medium-high heat until the butter melts. (I always use a stainless steel bowl set over a saucepan of boiling water. Make sure the water isn’t actually touching the bowl!)
While that’s going, beat the bejeezus out of your eggs in a separate bowl. I decided to do this by hand to see if I could (last time I tried to make it my arm got ridiculously tired), but I would recommend you use an electric mixer. The harder you beat the eggs, the more air you incorporate, the fluffier and lighter in color they become. You might want to know why you’re doing all this work – well, the lighter in color of the yolks, the less it will taste like eggs later on. Reason enough, right?
Back to the double boiler – Reduce the heat to medium so the water is simmering. Using a spoon, add a little bit of the super hot mixture into your eggs, and whisk vigorously. The reason you do this is so that the eggs can warm up a bit before you add them into the boiling lime mix. If your eggs are cold and the lime/sugar/butter are hot, you’ll cook your eggs and that’s not what you want. Keep adding some of the boiling lime juice into the eggs, slowly, until you’ve used about 1/4 cup. Make sure you mix it into the eggs quickly once it’s poured.
Now, you’re going to add the eggs back into the lime mix. This part is tricky, and it’s where it would come in handy to have a 3rd or even a 4th arm. Slowly pour the eggs into the double boiler with one hand, while mixing very quickly with the other. Even though you’ve tempered your eggs, there is still a chance they could cook if you leave them there too long. Once it’s all mixed together, stir occasionally as the curd starts to thicken. You’ll notice the change, and it will be ready when it is thick enough to coat the back of a wooden spoon. The directions said it takes about 20-25 minutes, but I don’t think it took me quite that long. I wouldn’t go by time with this, go by when it’s thick enough, and the spoon test is a really good gauge. (First pic is before, you can see it’s not sticking to the sides, kind of runny, second pic is after, you can see it’s thickened and lightened in color.)
Before you can put the curd into the fridge, you’ll want it to cool down a bit – especially since the bowl it’s in is super hot still. Using a strainer to squeeze out any lumps, transfer the mixture into a smaller bowl, I used another stainless, but you could use glass too, and set that bowl in another bowl or saucepan filled with ice water. You don’t want the ice water getting into the curd, so only fill it enough so the bottom of the bowl has any contact with it. When it’s cooler (you don’t have to let it cool all the way), wipe off the bottom of the bowl, and press plastic wrap up to the surface of the curd (not over the top of the bowl) before putting it in the fridge. If you have the wrap on the curd, it won’t form a skin on top.
Let it cool for a couple of hours, I left mine in overnight. I only used half of it to fill the 16 cupcakes, so there’s plenty leftover for future cupcake shenanigans.
Speaking of cupcakes… Here’s the recipe I adapted from The Joy of Cooking’s Sour Cream Cake (p714):
WHITE CHOCOLATE CUPCAKES
- 5 Tbsp butter
- 2/3 cup sugar
- 2 eggs – separated
- 1/8 tsp cream of tartar
- 1/2 tsp vanilla
- 1/2 cup sour cream
- 1/4 cup heavy cream
- 1/2 cup white chocolate chips
- 1 3/4 cups sifted cake flour (I used AP flour plus 1 3/4 Tbsp corn starch)
- 1 3/4 tsp baking powder
- 1/4 tsp baking soda
- 1/4 tsp salt
Quite the laundry list of ingredients, right? I’ll try to make this quick, since I know you’ve already been reading for a while. Melt the white chocolate chips and heavy cream in a double boiler. Keep the heat on medium-low. This will be good practice for when you have to do it again for the frosting. This step might take a bit, but while it’s melting you can do other things like…
Preheat your oven to 375F and line some muffin tins. I ended up with 16 cupcakes.
Then, after checking on your chocolate again to make sure it’s melting, sift together your dry ingredients – flour, baking powder, baking soda, salt – in a bowl. Then, in the bowl of the mixer, cream together your butter and sugar so they’re nice and light and fluffy. Check on your white chocolate to make sure the cream hasn’t formed a skin, make sure you smush it all around. I’ve noticed that white chocolate doesn’t really melt like regular chocolate does so you have to help it along with a spatula.
Next, beat in the 2 egg yolks along with the vanilla, scraping down the bowl as needed. You’re going to add the remainder of the ingredients with the dry-wet-dry method (flour mix in 3 parts, sour cream and white chocolate mix in 2 parts, start and end with dry ingredients).
Mix 1/3 of the flour into the butter mix. When it’s mostly incorporated, mix in your melted white chocolate (should be about 1/2 cup). Then add another 1/3 of your flour, followed by the sour cream, and finally the last of the flour. Beat until incorporated, because you’re going to mix the egg whites in momentarily and you don’t want to overmix.
So take your egg whites and cream of tartar in a separate bowl and beat them until they’re stiff. I did this by hand too, stupid idea, but you should definitely use a mixer if you have one. Once those are fluffy, take 1/3 of the whites and fold them into the batter. Once that has been mixed in completely, fold in the rest.
Divide your batter into 16 tins, they should each be about halfway full. These rose really nicely, so you shouldn’t feel the need to overfill each cup. Bake the cupcakes for 15-17 mins, until a toothpick comes out clean. If they look pale and sickly when time’s up, even if the toothpick is clean, you can leave them in a little longer to brown a bit on top.
Remove them to a wire rack to cool.
Now you should make your frosting because it will need to set for a bit in the fridge. (All the ingredients and directions can be found at that link.) One note I will make here is that I recommend using 2 cups of powdered sugar instead of just the one. First of all, I didn’t have enough frosting for all 16 cupcakes (only for 14 of them), but secondly because it contains a lot of butter and loses its shape pretty quickly.
Once the cupcakes have completely cooled, you can cut them open using the cone method and fill with about a Tablespoon of lime curd.
Once your frosting has been chilled, but not hardened or you’ll have to beat it again to get back to the right consistency, pipe some on top and you’re all set!
I hope you enjoy these cupcakes because all the hard work is worth the pleasure of eating them in the end. And please vote for these in the 2nd installment of the Mystery Box Cupcake Challenge hosted by Sweetest Kitchen because…
The winner of August’s Mystery Box Cupcake Challenge will receive prizes from:
- Bake It Pretty; $5 electronic gift card
- Beanilla; 3 Indian + 3 Tahitian vanilla beans & a jar of Ground Vanilla
- CT2Designs; a cupcake ring
- Miss Kitty Creations; a cupcake charm of your choice
- Sweet Cuppin Cakes; a prize pack worth $25
(Thank you to all our prize sponsors!)
And also because these are an experience every baker and sweet/tart-lover should have. Now feel free to ogle at some of the additional White Lime food porn I have included for you below: