- cooking spray
- 5 cups fresh blackberries
- 1/2 cup white sugar
- 2 tablespoons lemon juice
- 1 (15.8 ounce) package lemon-poppy seed muffin mix
- 1 egg
- 1/3 cup milk
- 1 teaspoon ground cinnamon
- 1/2 cup butter at room temperature
- 1 cup brown sugar
- Preheat oven to 375 degrees F (190 degrees C). Spray a 9×9-inch baking pan with cooking spray.
- Spread the blackberries into the prepared baking pan, and sprinkle with white sugar; drizzle with lemon juice. In a bowl, mix the lemon-poppy seed muffin mix, egg, milk, and cinnamon, and stir until moistened. It's okay to leave lumps in the batter. Pour the batter over the blackberries.
- Place the butter and brown sugar into a bowl, and mix with an electric mixer on medium speed until the mixture resembles coarse crumbs. Spread this mixture over the batter in the pan.
- Bake in the preheated oven until the topping is browned and the blackberries are bubbling, about 1 hour. Allow to stand for 20 minutes before serving.