Preheat your oven to 350 degrees F. Line a 9-inch x 13-inch baking pan with parchment paper and then grease the paper with non-stick cooking spray. Set aside.
In a medium mixing bowl, stir together the flour, baking powder, baking soda, and salt. Set aside.
In a large mixing bowl, beat together the sugar, eggs, vegetable oil, sour cream, and vanilla on low speed until well combined.
Add the dry ingredients to the wet ingredients and mix until just combined. Pour in the milk and mix. (Do not over mix or the cake will be dry.)
Pour the cake batter into the prepared pan. Bake for 32-35 minutes or until a toothpick inserted in the center comes out clean.
Remove the cake from the oven and let cool completely in the pan on a wire rack.
Frosting
In a large mixing bowl, beat together the powdered sugar, butter, and vanilla until light and fluffy, about 5 minutes.
Spread the frosting over the top of the cake in an even layer. Top with sprinkles if desired. Cut the cake into 12 slices (3x4 grid) before serving.
Notes
To measure the flour, put the measuring cup on the counter then use a spoon to scoop flour directly out of the bag and lightly place it into the cup. If you use the measuring cup to scoop directly from the bag, you’ll likely end up with 25% more flour than you actually need because the flour gets packed down into the cup. This will cause the cake to come out dry.
Store any leftovers in an airtight container at room temp for up to 3 days, in the fridge for up to 5 days, or freeze for up to 2 months.