
Heat oven to 375 degrees Fahrenheit.
Add blueberries, lemon juice, 2 tablespoons of flour, sugar, and pinch of salt to a 9-inch pie dish (or use a 2-quart baking dish). Toss well until combined.
Combine flour, oats, sugar, and the salt in a medium bowl. Add the melted butter then stir until all the flour has been moistened by the butter and topping is crumbly.
Sprinkle over blueberry filling. (We like to use our hands to do this. As we sprinkle, we press the crumbles together to create larger clumps of topping.)
Bake 25 to 35 minutes until juices are thickened and the topping has turned light golden brown. Cool 10 minutes, and then serve.