This recipe is slightly adapted from WinneAb’s Chocolate Chocolate Chip Cupcakes with Chocolate Sour Cream Frosting. I use a mix of all-purpose and whole-wheat flour, and I swap out some of the white sugar for brown sugar and maple syrup. A couple tips: First, make sure your sour cream is at room temperature when you mix it with the melted chocolate (otherwise, the chocolate will seize into clumps). Second, if you want to wrap and transport your cake, use toothpicks to construct a sturdy aluminum foil tent. You don't want to end up with a bare cake and heavily frosted foil. —Sarah Jampel
Preheat the oven to 350° F. Butter a 9- x 9-inch baking pan, line it with parchment paper, and butter the paper, too.
In a large bowl, mix together all of the dry ingredients (flour through salt).
In another bowl, mix together the wet ingredients (sour cream through vanilla extract).
Make a well in the center of the dry ingredients, add the wet ingredients, and fold with a rubber spatula until everything is just incorporated.
Fold in the chocolate chips.
Bake the cake for about 50 minutes, or until the center is set and a tester comes out clean.
For the frosting:
Once the cake has cooled completely, melt the chocolate chips in a double boiler or in the microwave.
Mix the melted chocolate chips and the room temperature sour cream using either a whisk, a stand mixer, or hand beaters.
Let the frosting cool slightly so that it thickens a bit. If it becomes too thick and clumpy for your liking, gently melt it in a double boiler or the microwave and whisk until smooth.
Use a rubber or offset spatula to frost the cake. I like to frost the top and the sides for the ultimate chocolate experience, but you can also just frost the top (which will make it much less messy to slice and eat).