Preheat oven to 350°. Spray two 9-inch cake pans with baking spray. Set aside. 

Whisk flour, baking powder, baking soda, and salt in a medium bowl. Set aside. 

Cream butter, brown sugar, and vanilla in the bowl of an electric mixer on medium-high speed until light and fluffy, about 5 minutes. 

Add eggs, one at a time, beating until well combined. 

Reduce the speed to low, add the flour in three batches, and alternate with the buttermilk. The batter will look curdled, but it will become smooth. 

Take the bowl off the mixer, add the sprinkles and gently fold through, also making sure that everything is well combined.

Divide the batter evenly between the two pans. Bake for 35 to 45 minutes, or until centers spring back and a toothpick comes out with a few crumbs. Let cool in pans for 10 minutes, then turn out and let cool completely on a wire rack. 

I used my Marshmallow Buttercream with lemon extract instead of vanilla bean to frost this cake.