Bring a smile to someone's face by celebrating their "half-birthday" with half of a birthday cake! One 9-inch vanilla funfetti cake, cut in half, stacked, and frosted to make a half-birthday cake.
Preheat oven to 350°F. Grease a 9-inch cake pan and set aside.
In a medium sized bowl, combine flour, baking powder, baking soda, and salt. Set aside
In a large bowl, whisk melted butter and sugar, until combined. Add egg, yogurt/sour cream, milk, and vanilla extract, whisk to combine. Slowly stir in the dry ingredients, mixing until they are just combined. Fold in the sprinkles, being careful not to over mix.
Pour the batter in to the prepared pan - the batter will be thick. Bake for 24-28 minutes, until the cake springs back when you touch it and a toothpick inserted into the center comes out clean. Cool completely on a wire rack.
For the frosting:
With a hand mixer or stand mixer, on medium speed, beat butter and powdered sugar for 2 minutes, until light and creamy. Add vanilla extract and 2 tablespoons of cream, and beat for another 2 minutes, scraping the sides of the bowl as necessary. If the frosting seems too thick, you can add another tablespoon of cream.
To assemble the cake:
Cut the cake in half. Using a butter knife or offset spatula, frost the top of one half and then place the other half on top of it. Continue frosting the rest of the cake. Pipe additional frosting around the borders, if desired. Garnish with sprinkles.