Preheat oven to 350°F (177°C). Grease and flour a 9-inch round cake pan and set aside.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
In a large bowl, beat together the sugar and butter until light and fluffy. Add the eggs one at a time, beating well after each addition. Beat in the vanilla.
Add the dry ingredients to the wet ingredients in three additions, alternating with the buttermilk and beginning and ending with the dry ingredients. Beat until just combined.
Stir in the rainbow sprinkles.
Pour the batter into the prepared pan and bake for 30-35 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Allow the cake to cool in the pan for at least 10 minutes before turning it out onto a wire rack to cool completely.
Interesting Facts
This birthday cake is great for any occasion, not just birthdays!
You can use any type of sprinkles you like - colorful, chocolate, or even crushed candy pieces.
This cake is best served the day it is made, but can also be stored in an airtight container at room temperature for up to 3 days.