Preheat oven to 350°F (177°C). Generously grease and lightly flour a 12×17-inch half sheet/jelly roll pan. Set aside.

In a large bowl using a handheld mixer or stand mixer fitted with a paddle attachment, cream the softened butter for about 1 minute on medium speed. Get it nice and smooth, then add the sugar on medium speed and beat until fluffy and light in color. Beat in eggs and vanilla until smooth. You’ll need to stop the mixer and scrape down the sides and up the bottom of the bowl to get it all mixed a couple times. Beat in the yogurt on medium high speed until combined.

In a large bowl, whisk the flour, baking soda, and salt together. Pour half of this flour mixture into the creamed butter mixture. Beat on low speed for 5 seconds. Pour in half of the milk. Beat on low speed for 5 seconds. Repeat with the rest of the flour and beat in the remainder of the milk until combined and smooth. Do not overmix. Fold in the sprinkles.

Spread the cake batter into the prepared pan. Smooth it out into a thin, even layer. Bake for 20-24 minutes or until the top is lightly browned and a toothpick inserted in the center comes out clean. Make sure you rotate the cake pan once or twice during bake time if your oven has hot spots (mine does). Remove from the oven and allow the cake to cool in the pan on a wire rack. As the cake is cooling, make the frosting.

Using a handheld mixer or stand mixer fitted with a paddle or whisk attachment, beat the butter on medium speed until creamy—about 2 minutes. Add confectioners’ sugar, milk, vanilla extract, and salt with the mixer running on low. Increase to high speed and beat for 3 full minutes. Add more confectioners’ sugar if frosting is too thin, more milk if frosting is too thick, or a pinch more of salt if frosting is way too sweet.

Spread frosting all over cooled cake, then top with sprinkles. Slice and serve. Cover leftovers tightly and store in the refrigerator for up to 5 days.