Preheat your oven to 350°F (175°C) and grease two 9-inch round cake pans.

In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt.

In a larger bowl, cream the unsalted butter and granulated sugar until light and fluffy.

Add eggs one at a time, mixing well after each, then add vanilla extract.

Gradually add the dry ingredients to the wet mixture, alternating with the buttermilk.

Divide batter into the prepared pans and bake for 25-30 minutes.

Allow cakes to cool in their pans for about 10 minutes, then transfer to a wire rack.

For the raspberry filling, combine fresh raspberries, lemon juice, and sugar in a saucepan and cook until thickened.

For the buttercream, whisk egg whites and powdered sugar over simmering water until sugar dissolves, then whip to stiff peaks.

Level the cooled cake layers, spread raspberry filling and buttercream between them, then stack.

Apply a crumb coat of buttercream and chill for 30 minutes.

Finish with a thicker layer of buttercream, smooth the sides, and decorate as desired.