Preheat your oven to 350F. Grease in your baking pan. In a big bowl, combine your baking powder together with your flour. Then add your salt.
In larger bowl, cream together butter and sugar until it becomes fluffy. You can now add your flour mix.
In a smaller bowl, stir the milk, eggs and vanilla extract together. Then add these wet ingredients to the butter/flour mixture. Beat on low speed until they are all well incoprporated.
Here comes the Funfetti part: fold the rainbow sprinkles using a spatula and then pour the batter inside the prepared pan. Just add a few sprinkles at the top of the cake. And bake for about 45 minutes, until the toothpick inserted into the center of the cake comes out clean.
You should then allow your already baked cake to cool down before removing it from your pan.