Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans, or line them with parchment rounds.

In a large bowl, beat 1/2 cup softened butter with 1 1/2 cups granulated sugar until the mixture is light and fluffy, about 3 to 4 minutes.

Add the eggs one at a time, mixing well after each addition, then stir in 1 teaspoon vanilla. Scrape the bowl as needed.

In a separate bowl, whisk together 2 cups flour, 3 1/2 teaspoons baking powder, and 1/2 teaspoon salt.

Add the dry ingredients to the butter-egg mixture in three parts, alternating with 1 cup milk. Begin and end with the dry ingredients. Mix just until combined; do not overmix.

Divide the batter evenly between the prepared pans and smooth the tops with a spatula.

Bake for 25 to 30 minutes, or until a toothpick inserted in the center comes out clean and the tops spring back lightly when pressed.

Let the cakes cool in the pans for 10 minutes, then run a knife around the edges and turn them out onto wire racks to cool completely.

For the frosting, beat 1 cup softened butter until creamy. Gradually add 2 cups powdered sugar until mostly incorporated. Mix in 2 teaspoons vanilla and 1 to 2 tablespoons milk until the frosting is light and spreadable. Taste and adjust for sweetness or consistency.

Level the cake layers if needed. Place one cooled layer on your serving plate, spread a layer of frosting, top with the second layer, then frost the top and sides.

Sprinkle sparkling sugar lightly over the top for decoration. Slice and serve at room temperature for best texture.