Preheat oven to 350 degrees. Zest and juice lemon. Prepare a 9x9 baking dish by greasing it with 2 tablespoons butter.
Combine filling ingredients. In a large bowl gently toss blueberries with cornstarch, sugar, salt and lemon juice until berries are coated.
¼ cup cornstarch, ¼ cup granulated sugar, ½ teaspoon salt, 1 teaspoon lemon juice, 4 cups blueberries
Pour blueberry lemon filling into baking dish.
Then make the blueberry crisp topping. Add oats, brown sugar, almonds, lemon zest and coconut flakes to medium bowl. Then work in softened butter until butter is evenly distributed making for a crumbly dough that stays together when squeezed.
½ cup oats, ½ cup roasted almonds, ½ cup unsalted butter, ¼ cup unsweetend flaked coconut, 1 teaspoon lemon zest, ¼ cup light brown sugar
Evenly scatter almond crumb topping over filling. Then dot with remaining 2 tablespoons butter.
Bake uncovered in preheated oven until lightly browned and bubbly, about 35-40 minutes.
Remove from oven and let sit 5 minutes before serving.
Notes
Frozen berries can be substituted. Defrost and drain before using or use frozen by doubling the cornstarch to ½ cup and increasing the cooking time by 15-20 minutes.