Spray an 8-inch baking dish with cooking spray and preheat the oven to 375.
Put blueberries in the baking dish and mix in vanilla, lemon juice and zest. Sprinkle in sugar, flour (the 1/2 teaspoon), salt, and stir in melted butter. Set aside.
Now for the topping! In a sperate bowl, stir together flour, baking powder, and sugar. Cut in chilled butter until it resembles a coarse sand (I use my hands). Make a well in the center and pour in milk and vanilla, stir until just wet. Cover and set aside for 10 minutes.
Spoon the batter over the blueberries. Mix cinnamon and sugar and sprinkle on top.
Bake for 30 minutes or until top is golden, checking at 25 minutes. Cool but serve warm with ice cream on the side.