Preheat your oven to 350°F and line a 12-cup muffin tin with paper liners. In a small bowl, mix together the flour, baking powder, and salt — this prevents lumps from sneaking into your batter. Set this dry mixture aside for a minute, and don't skip sifting if you have the time.

In a large mixing bowl, cream together the softened butter and granulated sugar until it looks pale and fluffy, about 3 minutes with an electric mixer. This step matters because it incorporates air into your vanilla cupcakes recipe. Stop and scrape down the bowl halfway through so everything blends evenly.

Add the eggs one at a time, beating well after each addition so they fully incorporate into the butter mixture. The batter should look creamy and smooth at this point. If it looks kinda curdled, don't panic — it'll come together once you add the dry ingredients.

Gently fold in half the flour mixture using a spatula, stirring just until combined without overworking it. Pour in half the milk mixed with Greek yogurt, then fold in the remaining flour mixture. Finish with the last of the milk mixture, folding until you don't see dry flour streaks anymore.

Scrape the vanilla bean seeds into the batter and fold them in so they distribute throughout. The black specks give these birthday cupcakes that homemade look. Divide the batter evenly among the 12 liners, filling each about two-thirds full.

Bake for 18 to 20 minutes until a toothpick inserted in the center comes out clean or with just a few crumbs. The tops shouldn't be dark brown — they should look light golden. I always set a timer at 18 minutes and check because ovens vary wildly, and I've definitely overcooked a batch before.

Let the cupcakes cool in the pan for 5 minutes, then turn them out onto a wire rack to cool completely before frosting. This takes about 30 minutes total, but you can speed it up by putting them in the fridge for 10 minutes if you're impatient like me. Once they're cool, beat softened butter with powdered sugar until fluffy and pipe or spread onto each cupcake.