Place blueberries, lemon zest, lemon juice, granulated sugar and flour in a mixing bowl. Toss gently so the berries are covered with the flour and sugar.
5 cups blueberries, ⅓ cup granulated sugar, 3 tablespoons flour, 1 zest from one lemon, 1 tablespoon lemon juice
Put berries into a greased 8x8 inch baking dish.
Topping
Using the same bowl, put oats, flour, brown sugar, cinnamon and salt and toss lightly.
¾ cup oats, ¼ cup flour, ¼ cup brown sugar, ½ teaspoon cinnamon, ⅛ teaspoon salt
Add melted butter and stir until the oats are coated.
¼ cup butter
Place oats over the blueberries and spread evenly across the top.
Bake in a preheated 375°F oven for 35-40 minutes, until the topping is golden and the center of the blueberries is bubbly.
Notes
If using frozen blueberries, don't thaw. Add frozen and increase baking time by 10-15 minutes.
If the topping browns too much, place a piece of foil loosely over the top until the filling is bubbly.
The filling has to be bubbly for it to thicken. Keep in mind, that this won't become very thick like a pie or jam. If you prefer a thicker filling, add another tablespoon of flour.
Eat warm or at room temperature.
Store cool crisp covered at room temperature for 2-3 days or in the refrigerator for 3-4 days.
Blueberry crisp variations
Make it a peach blueberry crisp! Add 1-2 cups of sliced peaches to the mixture. Mix in an additional 2 tablespoons of flour.
Add a chopped, tart apple to the filling. Peel and cube an apple and bake until the apples are soft.
Use wild huckleberries instead of the blueberries.
Add ½ cup of chopped walnuts or pecans to the topping.