Preheat your oven to 350°F (175°C) and prepare three 9-inch round cake pans by greasing and flouring them.

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

Cream the softened unsalted butter and granulated sugar together until light and fluffy, about 3 to 5 minutes.

Add the eggs one at a time to the creamed butter mixture, mixing well after each addition, then add the vanilla extract.

Gradually mix the flour mixture into the creamed mixture, alternating with the buttermilk.

Divide the batter among the prepared cake pans and bake for 25 to 30 minutes.

Allow the cakes to cool for about 10 minutes in the pans before transferring to wire racks to cool completely.

In a saucepan, combine fresh raspberries, sugar, and lemon juice over medium heat until mixture thickens.

For the buttercream, combine egg whites and granulated sugar in a heat-proof bowl over a double boiler, whisk until warm, then whip until glossy peaks form, adding softened butter.

Level the cooled cake layers if needed, then stack with buttercream and raspberry filling between layers.

Apply a crumb coat of buttercream around the cake and chill in the refrigerator for about 30 minutes.

After chilling, apply a final coat of buttercream and decorate with fresh raspberries or edible flowers.