Yellow Cake with Chocolate Frosting

 

2 C. (256 grams) cake flour (not self-rising)

2 tsp. (8 grams) baking powder

½ tsp. (3 grams) fine sea salt

8 T. (112 grams) unsalted butter, softened

1 C. (200 grams) sugar

3 large eggs, left at room temperature for 30 minutes

1 ½ tsp. (7 ml) vanilla extract

¾ C. (177 ml) whole milk

For the chocolate frosting

5 ounces (142 grams) semi-sweet chocolate chips

½ C. (120 grams) sour cream

1 T. (15 ml) whole milk

1 tsp. (5 ml) vanilla extract

Pinch of fine sea salt

Rainbow sprinkles

 

Preheat oven to 350°F with a rack in the center. Butter and flour an 8 x 8-inch baking pan, tapping out any excess flour. Into a medium mixing bowl, sift together the flour, baking powder, and salt. In a large mixing bowl or the bowl of a stand mixer fitted with the whisk, beat butter and sugar together on medium-high until pale and fluffy, about 5 minutes. Beat in the eggs one at a time until incorporated. Add vanilla and beat for 5 minutes more. Reduce mixer speed to low and alternate between adding the flour mixture (in 3 parts) and the milk (in two parts), starting and ending with flour. Mix just until batter is smooth — do not overmix. Spread batter into pan and bake for 30-35 minutes, just until a cake tester comes out clean from the center. Cake will be pale, not brown. Cool completely before frosting. For the chocolate frosting Melt the chocolate chips in a double boiler or in short bursts (about 30 seconds each) in the microwave, stirring between bursts. When melted, stir in sour cream, milk, vanilla and salt until smooth and glossy. Spread immediately onto cooled cake. Decorate with sprinkles. Frosting will set over time.