Name: Birthday Cake Pebbles Surprise Cake
Ingredients: 3 cups whole milk; 6 cups Post Birthday Cake Pebbles, divided, plus more for garnish; Cooking spray; 3 ¾ cups cake flour, sifted; 1 Tbsp. baking powder; ¾ tsp. baking soda; 2 ½ Tbsp. vanilla extract, divided; 1 ½ tsp. salt; 3 cups + 1 Tbsp. unsalted butter, room temperature, divided; 5 large eggs, room temperature; 2 cups granulated sugar; ½ cup sour cream, room temperature; 7 cups powdered sugar; ¼ tsp. salt; 2 cups assorted sprinkles