Melt butter and allow to cool. Set aside.
In the large bowl, use an electric hand mixer to beat eggs and egg yolk until light in color. Slowly add sugar and continue to beat until mixture is thick and pale in color, about 3-5 minutes. Stir in vanilla.
In another bowl, whisk together flour, malted milk powder, baking powder, and salt. Use a spatual to gently gold dry ingredients in egg mixture.
Add cooled melted butter in two additions. Fold until butter is fully absorbed into batter. Trasnfer batter to an airtight contianer. Let chill in the fridge for at least three hours, preferably overnight.
Preheat oven to 375° F. Butter and flour a 12 cavity madeline pan. Tap out excess flour.
Fold confetti sprinkles into chilled batter.
Fill madeleine pan ¾ full of batter. Use a piping bag, small cookie scoop, or two spoons to distribute the batter.
Bake for 10-12 minutes until cakes have a little hump and the top of cake springs bake when gently pressed. Allow cakes to cool in pan for one minute before inverting and unmolding. Allow cakes to cool before dipping in white chocolate.