Preheat oven to 350 degrees F. Generously grease and flour a 9-inch round pan. Set aside.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

In a large microwave-safe bowl, melt the 1 stick of butter in the microwave. Whisk in both white and brown sugars vigorously until no lumps remain – mixture will be gritty. Whisk in the egg, yogurt, milk, and vanilla extract until combined.

Slowly mix this wet mixture into the dry flour mixture until no lumps remain. Batter will be thick.

Slowly fold in sprinkles, but do not overmix because that will cause the sprinkles to bleed their color into the batter.

Pour the batter into the prepared cake pan.

This cake takes around 33-36 minutes to bake. What I suggest is to bake it for 20 minutes, then cover loosely with aluminum foil (loosely to avoid the top from sticking to the foil) and continue baking for 13-16 more minutes or until a toothpick inserted in the center comes out clean.

Allow to cool for 10 minutes in the pan, and then turn the cake out onto a cooling rack and let it cool completely.

In a large bowl, with a hand or stand mixer, cream together sugar and butter on low speed. Mix until well blended. Increase speed to medium and beat for another 3 minutes. Add vanilla and cream and continue to beat on medium speed for 1 minute more, adding more cream if needed for desired consistency.

Once cake is completely cool, spread the buttercream evenly on cake + decorate with more sprinkles, if desired.