Preheat oven to 350 F. Generously butter five wells in a muffin tin.

In the bowl of a stand mixer, beat together the butter and sugar until light and creamy. Add the egg and vanilla, and beat until incorporated.

Add in the dry ingredients and switch to a spatula or wooden spoon to gently mix the ingredients together just until the flour streaks disappear. The batter will be thick.

Scoop the batter into the buttered muffin tins, smoothing down the tops.

Bake for about 20 minutes, or until a toothpick inserted in the center comes out clean. The edges of the cakes will be golden brown.

Remove from the oven and cool completely on a wire rack. Use a knife to gently loosen the edges and bottom of the cakes from the wells to release them.

Slice the cakes in half, and fill with vanilla buttercream.

Note: I chose to slice the domes off the top of the cakes to make them flat, but this is optional.

Add all of the ingredients to a stand mixer and beat until the buttercream is nice and fluffy, about 3-5 minutes. If the buttercream is too thick, add a bit more whipped cream. If it's too thin, add more powdered sugar. You want it to have a good piping consistency.

Pipe the buttercream onto both the top and bottom cake halves, and place raspberries along the edges of the bottom cake, spacing them out evenly.

Place the top cake half on top like a sandwich.

Pipe buttercream on the top of the cakes, and dust with powdered sugar.

Decorate with a cut rosemary stem, if desired.