Step 1

Preheat the oven to 375 degrees Fahrenheit.

Step 2

Make the filling: In a medium bowl, mix the blueberries, 1/2 cup sugar, cornstarch, 1/2 teaspoon cinnamon, allspice, and lemon zest. Pour into a round 9-inch pie pan, 9 x 9 inch baking dish or 7 x 11 baking dish.

Step 3

Make the topping: In a medium bowl, add the remaining 1/2 cup sugar, 1/2 teaspoon cinnamon, flour, baking powder and kosher salt. Mix together with a fork. Pour in the melted butter while mixing with the fork until a crumbly mixture forms. Use your fingers to sprinkle the crumbles evenly over the filling.

Step 4

Bake: Bake for 45 to 50 minutes until the top is evenly golden brown and the filling is bubbly. Cool for 1 hour, then serve. You can leave it out on the counter for up to 1 day (covered, at night) so the topping can stay crisp. After 1 day, refrigerate any leftovers. It also freezes well for several months in a sealed container; reheat it in a 350 degree oven until bubbly.