Iron Skillet Mixed Berry Crisp

Amber from 98.5 The Bull has a tasty recipe for an Iron Skillet Mixed Berry Crisp.

3 cups fresh blueberries  

3 cups fresh raspberries 

3 cups fresh blackberries  

1/3 cup granulated sugar 

1/3 cup all-purpose flour  

Grated zest of 1 lemon 

3 tablespoons pineapple juice 

For the Topping: 

1/2 cup granulated sugar 

1/2 cup packed light brown sugar 

3/4 cup all-purpose flour 

3/4 cup old-fashioned oats 

1 teaspoon ground cinnamon 

Pinch of salt 

1 stick cold unsalted butter, cut into squares 

1.  Preheat the oven to 375 degrees F. Grease a 12-inch cast-iron skillet with butter and set aside. In a mixing bowl, combine the berries, granulated sugar, flour, lemon zest and pineapple juice. Pour into the pan and smooth into an even layer. 
2.  In another mixing bowl, mix both sugars, the flour, oats, cinnamon and salt. Cut in the butter until you have a coarse crumb. Sprinkle this mixture evenly and loosely over the top of the berries. Bake, uncovered, until golden brown, crisp and bubbling, 35 to 40 minutes. Remove from the oven and let sit at least 10 minutes before serving.