Classic Yellow Cake with Chocolate Frosting

Arrange a rack in middle of oven; preheat to 350°F. Lightly coat cake pans with nonstick spray. Line bottom of pans with parchment paper; lightly coat parchment with nonstick spray.

Whisk flour, baking powder, and salt in a medium bowl. Stir milk and vanilla in another medium bowl.

Using an electric mixer on medium speed, beat granulated sugar and butter in a large bowl, scraping down sides as needed, until light and creamy, about 5 minutes. Add yolks in 2 additions, scraping down bowl after each. (Batter may separate slightly; it will come back together after dry ingredients are added.)

Reduce mixer speed to low and add dry ingredients in 3 additions, alternating with milk mixture in 2 additions, beginning and ending with dry ingredients; beat until smooth. Divide batter between prepared pans (slightly less than 3 cups per pan); smooth top.

Bake cakes, rotating pans halfway through, until light golden brown, the centers spring back when gently pressed, and a tester inserted into the centers comes out with a few moist crumbs attached, 30–35 minutes.

Transfer cakes to wire racks; let cool in pans at least 15 minutes. Invert cakes onto racks, peel off parchment, and let cool completely.

Using a long serrated knife, trim top dome and any bumps from each cake to create a flat surface.

Using an electric mixer on high speed, beat butter in a large bowl until smooth, about 30 seconds. Reduce mixer speed to low and add powdered sugar, 1 cup at a time, scraping sides and bottom of bowl often. Increase mixer speed to medium and add cocoa powder and salt, then add milk and vanilla. Continue to beat until light and fluffy, 2–3 minutes. Cover and store at room temperature until ready to use.

Spread 1 Tbsp. frosting in the center of a platter. Place 1 cake layer, top side down, in the center. Evenly spread 1 1/2 cups frosting on top of cake with an offset spatula, pressing frosting outward toward edges. Carefully place second cake layer, top side down, over, gently pressing down to secure. Evenly spread 2 cups frosting over top and sides. Chill at least 15 minutes to let frosting set.

Spread remaining 2 cups frosting over top and sides, swirling decoratively, making sure to cover bottom of platter. Top with sprinkles, if desired. Chill at least 30 minutes or up to overnight to let frosting set.

Cake can be made 3 days ahead; wrap tightly in plastic and chill, or freeze up to 2 weeks. Frosting can be made 3 days ahead; cover with plastic wrap, pressing directly on surface, and chill. Bring to room temperature before using.