• Preheat oven to 350°F (175–180°C). Line pan with parchment.
• Cream the 14 Tbsp salted butter with the 1 cup sugar until light and fluffy. Scrape down the sides and bottom of the bowl a few times during the process.
• Beat in 3 large eggs one at a time, scraping down the sides of the bowl as needed, then add the 1 Tbsp vanilla extract.
• Whisk 1 2/3 cups all-purpose flour and 2 tsp baking powder together, then fold in just until no dry spots remain.
• Spread smoothly into your baking pan.
• Bake 25-30 minutes, until lightly golden and springs back in center. Let cool before frosting.
• Make the icing by stirring together the 1 1/2 cups confectioners sugar and 2 Tbsp milk or more as needed to form a smooth glaze. Spread over the cooled cake and let sit for a couple of minutes before adding the sprinkles. Let set before slicing.
• Serve each piece of cake in a shallow bowl on top of a little puddle of custard.

make the custard

• In a bowl whisk the 2 egg yolks, 1 Tbsp cornstarch and 1/4 cup sugar until well combined. Heat the 1 1/4 cups whole milk in a saucepan until it starts to steam. Pull off the heat and drizzle some of the hot milk into the bowl, whisking constantly. Pour the bowl into the pan, still whisking, and return to the stove. Cook gently until the custard starts to thicken and coats the back of a spoon. Do not let it boil. Stir in the 1/2 tsp vanilla extract and strain through a sieve to catch any lumps. The custard can be served warm, or chilled.