Preheat the oven to 350°F (180°C) and butter and flour a 13 x 18-inch (33 x 46-cm) half-sheet pan. Set aside.

In the bowl of a stand mixer fitted with a paddle attachment or in a medium bowl with a handheld electric mixer, beat the butter and sugar together on medium-high speed for 3 minutes, until fluffy.

Add the eggs, one at a time and scraping down the bowl after each addition. Beat in the milk and vanilla extract.

In a medium bowl, whisk the flour, baking powder, and salt together, then fold into the butter mixture until evenly mixed.

Spread evenly in the prepared pan and bake for 20 minutes or until a toothpick inserted in the center comes out clean.

Let cool completely before frosting with Vanilla Buttercream. Store in an airtight container at room temperature for up to 2 days.