Preheat the oven to 350 degrees. Coat an 8 × 8 baking dish with cooking spray.
Cream the butter, sugar, and lemon zest together with a hand mixer or stand mixer until smooth and creamy.
Add the egg and vanilla and beat until combined.
Mix the flour, baking powder, and salt until well combined.
Add the flour mixture to the butter mixture a little at a time, alternating with the buttermilk, and gently fold in most of the raspberries. Side note: The batter will be very thick.
Spread batter into the pan evenly. Gently push the remaining few raspberries into the top of the cake in places that need them.
Sprinkle 1-2 tablespoons of sugar evenly on the batter.
Place into the oven and bake for 40-45 minutes or until a tester inserted into the center of the cake comes out clean.
Let it cool for at least 10-15 minutes before cutting and serving. Enjoy!