Line a 12-cup muffin tin with cupcake liners.

In a large bowl, beat the butter and granulated sugar together using an electric mixer or a stand mixer until light and fluffy, about 5 minutes. Beat in the 2 eggs one at a time; add the 1 teaspoon pure vanilla extract.

In another large bowl, whisk together the flour, baking powder and fine sea salt. With the mixer on low, add half the flour mixture to the butter and egg mixture and beat until just combined. Add the buttermilk and mix well to combine. Add the remaining flour mixture and beat until just combined, scraping down the bowl as necessary. Fold in the sprinkles.

Divide the batter equally between the prepared cups. Preheat the oven to 350 and rest the batter while the oven heats.

Bake for 30-35 minutes, until a tester inserted in the middle of the cake comes out clean. Remove from oven and place on a rack to cool for 15 minutes, then turn the cake out onto the rack to cool completely.

In a large bowl, beat the butter until light and fluffy. Sift in the powdered sugar, then add the vanilla, and beat well to combine. Add a teaspoon or 2 of milk if needed. You can beat in the sprinkles or sprinkle them on top.

Frost each cupcake with a generous swirl of frosting and top with more sprinkles if desired.