Best Yellow Layer Cake (adapted from Smitten Kitchen)
Yield: Two 9-inch round, 2-inch tall cake layers
4 cups plus 2 tablespoons (480 grams) cake flour (not self-rising)
2 teaspoons (10 grams) baking powder
1 1/2 teaspoons baking soda
1 teaspoon (5 grams) table salt
2 sticks (1 cup, 1/2 pound or 225 grams) unsalted butter, softened
1.5 cups sugar
2 teaspoons (10 ml) pure vanilla extract
4 large eggs, at room temperature
2 cups buttermilk (475 ml), well-shaken
Preheat oven to 300°F. Butter and flour two 9-inch round cake pans.
Sift together flour, baking powder, baking soda, and salt in a medium bowl. In a large mixing bowl, beat butter and sugar in a large bowl with an electric mixer at medium speed until pale and fluffy, then beat in vanilla. Add eggs 1 at a time, beating well and scraping down the bowl after each addition. At low speed, beat in buttermilk until just combined (mixture will look curdled). Add flour mixture in three batches, mixing until each addition is just incorporated.
Spread batter evenly in cake pan, then rap pan on counter several times to eliminate air bubbles. Bake until golden and a wooden pick inserted in center of cake comes out clean, about 45 minutes. Cool in pan on a rack 10 minutes, then run a knife around edge of pan. Invert onto rack and discard parchment, then cool completely, about 1 hour. Optional: while cake is still warm, brush some water or simple syrup onto the cakes to make sure your cakes are moist later.
Chocolate Sour Cream Frosting
Adapted from The Dessert Bible
Makes 5 cups of frosting, or enough to frost and fill a two layer 9-inch cake
15 ounces semisweet or bittersweet chocolate, chopped
2 1/4 cups sour cream, at room temperature
1/4 to 1/2 cup light corn syrup (I boiled about 3/4 c water with a LOT of sugar)
3/4 teaspoon vanilla extract
additional warm water to thin out the frosting, if needed
Melt chocolate over low heat. Remove from heat and let chocolate cool until tepid.
Whisk together the sour cream, 1/4 cup of the corn syrup and vanilla extract until combined. Add the tepid chocolate slowly and stir quickly until the mixture is uniform. Taste for sweetness, and if needed, add additional corn syrup in one tablespoon increments until desired level of sweetness is achieved.
Let cool in the refrigerator until the frosting is a spreadable consistency (about 30 minutes). If the frosting is very stiff, even after you leave it outside to warm up, whisk in some warm water until it becomes spreadable.