• Pre-heat oven to 350 degrees and line a cupcake tin with 12 papers.
• In a medium bowl, whisk together flour, baking powder, and salt.
• In the bowl of a stand mixer or in a large bowl with a hand mixer, cream together butter and sugar on medium-high speed until light and fluffy, about 3 minutes.
• Add eggs in one at a time, mixing well after each addition. Mix in vanilla extract.
• With mixer on low speed, beat in dry ingredients in 2 additions, alternating with the milk. Mix in each addition until just incorporated. Gently fold in rainbow sprinkles.
• Fill cupcake liners about ¾ of the way with batter. Bake cupcakes for 17-20 minutes, until edges are golden and tester comes out clean.
• Let cupcakes cool in tin for 5 minutes before moving to wire racks to cool completely.
• Once cupcakes are completely cool, core out a small section from the middle (either using a cupcake corer or with a knife). Fill center of cupcake with champagne custard.
• Fill a pastry bag with buttercream frosting, fit with pastry tip (I like to use a Wilton 2A) and frost cupcakes. Top with additional sprinkles.

Champagne Custard

• In a double boiler set over medium heat (or in a heat-proof bowl set securely over a saucepan of gently boiling water), whisk all the ingredients together. Cook for about 10-12 minutes while intermittently whisking, until mixture thickens.
• Remove from heat and place custard in fridge to cool completely. Custard will continue to thicken as it cools.

Vanilla Champagne Buttercream

• In the bowl of a stand mixer or in a large bowl with a hand mixer, beat butter until creamy, 1-2 minutes.
• With mixer on low, slowly blend in the confectioner’s sugar, cup by cup until well-combined.
• Mix in champagne and vanilla until combined.