Heat oven to 350°F. Grease and line a 9 x 13 inch pan with parchment.

Brown the butter in a saucepan until golden with toasty bits at the bottom. Cool to room temperature.

Whisk flour, baking powder, and salt in a bowl.

In another bowl, whisk sugar, eggs, milk, sour cream, vanilla, and cooled brown butter.

Stir dry into wet until just combined. Fold in sprinkles. Spread into pan.

Bake for 28 to 34 minutes until a toothpick comes out clean. Cool in pan.

Mix flour, sugar, salt, vanilla, and melted butter with a fork until clumps form. Stir in sprinkles.

Bake on a sheet at 300°F for 12 to 15 minutes until dry and lightly golden. Cool.

Mix milk and vanilla. Poke the cooled cake gently with a skewer and brush the milk soak over the top. Let it sit for 10 minutes.

Beat butter and cream cheese until smooth and fluffy, about 2 minutes.

Add powdered sugar, salt, and vanilla. Beat until creamy.

Add heavy cream and whip until light and spreadable.

Spread frosting over the cake. Spoon small puddles of warmed jam on top and gently swirl with a butter knife.

Sprinkle confetti crumbs over everything. Add extra sprinkles if you want to go full party mode.