Cream butter and sugar until light and fluffy. Add eggs, buttermilk, and vanilla. Lightly beat until blended.
Sift or wisk together in seperate bowl. Then add dry mixture to liquid and stir until flour disappears.
Gently stir berries into batter and fill muffin cups to the top.
Bake 20 minutes. Let cool 5 minutes. Remove from muffin tin and cool on baking rack.