Preheat oven to 350°F. Coat a 11x7" pan with cooking spray.
In a mixing bowl add the flour, sugar, baking powder, salt, and milk. Whisk to combine. Add the melted butter and vanilla and whisk until combined and a smooth batter.
Scatter 2 cups of berries on bottom of pan and pour batter evenly over top. Sprinkle remaining cup of berries on top, zest from half the lemon and finishing sugar.
Bake for 40-45 minutes, until golden brown. Serve warm with a scoop of ice cream or whipped cream.
Video
Notes
I use fresh berries, if using frozen, then thaw and drain excess liquid (drink it)!
Finishing sugar is crystalized sugar that is used in baked goods as a topping. It's crunchy, but feel free to substitute sugar if you can't find it.