Gather all ingredients and preheat the oven to 375 degrees F (190 degrees C).
Mix blueberries, sugar, and juice in a 7x11-inch baking dish. Set aside.
4 cups fresh or frozen blueberries, 3 tablespoons fresh lemon juice or orange juice, 1/4 cup granulated sugar
Cream butter and 1/2 cup sugar in a large bowl until light and fluffy.
1/2 cup salted butter, 1/2 cup granulated sugar
Beat in egg and vanilla.
1 large egg, 1/2 teaspoon vanilla extract
Add flour, baking powder, cinnamon, and salt, stirring just until combined.
1 cup all-purpose flour, 1/2 teaspoon baking powder, 1/4 teaspoon ground cinnamon, 1 pinch salt
Drop spoonfuls of batter over the blueberry mixture, covering as much filling as possible.
Sprinkle coarse sugar over the top.
Bake for about 35-40 minutes, until topping is golden brown and filling is bubbling.
Notes
Blueberries: If using frozen blueberries, don't thaw before use.
Lemon juice: I highly recommend using fresh lemon juice as bottled lemon juice can have an off taste. I recommend fresh orange juice, but bottled orange juice will work in a pinch.
Butter: I use salted butter. If using unsalted butter, add 1/4 teaspoon of salt along with the butter.
Coarse sugar: The coarse sugar adds a bit of sweetness and crunch.