Heat the oven to 350°F (175°C). Grease two 8-inch round cake pans, line the bottoms with parchment, and lightly flour the sides so the baked layers release cleanly.

Whisk the flour, baking powder, and fine salt together in a medium bowl. This distributes the leavening evenly and helps prevent salty or dense pockets in the finished cake.

Beat the softened butter and granulated sugar on medium speed for about 3–4 minutes, until pale and fluffy. Add the room-temperature eggs one at a time, beating well after each addition, then mix in the vanilla extract.

Add the dry ingredients in three additions, alternating with the buttermilk in two additions. Mix only until the batter is combined, scraping down the bowl as needed so no dry streaks remain.

Divide the batter evenly between the prepared pans and smooth the tops. Bake for 25–30 minutes, until the tops spring back lightly and a toothpick inserted in the center comes out clean or with a few moist crumbs.

Cool the cakes in their pans for 10 minutes. Turn them out onto cooling racks, remove the parchment, and let them cool completely before adding buttercream.

For the buttercream, beat the softened butter until smooth. Gradually add the sifted confectioners’ sugar, then mix in the vanilla and salt before adding the cream or milk.

Beat the buttercream for 2–3 minutes, until light and spreadable. Add a little more cream or milk if needed to reach a smooth frosting consistency.

Place one cake layer on a serving plate and spread it with buttercream. Add the second layer, frost the top and sides, and decorate with sprinkles if desired.