Preheat oven to 350°F. Grease a 9x13 pan. I recommend using a glass pan.
In a large bowl, stir together the wet ingredients: milk, oil, vinegar, vanilla.
In a separate bowl, whisk together the dry ingredients: flour, sugar, baking powder, baking soda, salt, and sprinkles.
Mix the dry ingredients into the wet ingredients. I use a whisk to reduce clumps and a rubber spatula to scrape the sides and bottom of the bowl.
Pour the batter into the cake pan.
Bake for 32-36 minutes, or until a toothpick comes out clean when stuck into the center of the cake.
Remove from the oven and let cool completely before removing from the pans. After 15 minutes of cooling at room temperature, you can put the cake pans in the fridge to speed up the process.
Frosting:
Using a stand mixer or hand mixer, whip the room temperature butter for about 2 minutes at medium speed. This step helps to aerate the butter and create a fluffy frosting.
Mix in the vanilla extract and 2 tablespoons of milk to start.
Beat in the powdered sugar 1 cup at a time at low speed until frosting is smooth.
Add more milk if the frosting is too thick, or more powdered sugar if too thin.