Confetti Cake With Chocolate Frosting

Name: Confetti Cake With Chocolate Frosting
Ingredients: ¾ cup (1½ sticks) unsalted butter, room temperature, cut into 1 pieces, plus more for pans; 3 large eggs, room temperature; ½ cup plus 2 Tbsp. whole milk; 2¼ cups (281 g) bleached cake flour; 1½ cups (300 g) granulated sugar; 2 tsp. baking powder; 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt; ¼ tsp. baking soda; ½ cup (115 g) sour cream; 1 Tbsp. vanilla bean paste or vanilla extract; ¼ tsp. almond extract; ½ cup rainbow sprinkles or confetti quins; 12 oz. milk chocolate, chopped (preferably Guittard); 12 oz. semisweet chocolate, chopped (about 50% cacao; preferably Guittard); 2½ cups sour cream, room temperature; 1½ tsp. Diamond Crystal or 1 tsp. Morton kosher salt; 1 tsp. vanilla bean paste or vanilla extract; Rainbow sprinkles or confetti quins (for decorating)