Place blueberries and sliced strawberries in a bowl with sugar, flour, and lemon juice. Toss together.
2 cups sliced strawberries, 2 cups blueberries, ⅓ cup sugar, ¼ cup flour, 1 tablespoon lemon juice
Then add raspberries and gently fold them in.
2 cups raspberries
Place berries in a lightly greased casserole dish.
Using the same bowl, mix the flour, sugar, baking powder, and salt.
1 cup flour, 1 tablespoon sugar, 1 ½ teaspoons baking powder, ¼ teaspoon salt
Cut in butter using your fingers or a pastry blender. The mixture should resemble coarse crumbs.
4 tablespoons butter
Mix in milk. Stir just until everything is mixed together.
½ cup milk
Take large spoonfuls of the biscuit dough and drop directly onto the berries. I try to make biscuits on top of the berries, one for each serving.
Sprinkle a bit of sugar over the top of each biscuit.
½ teaspoon sugar
Bake in a preheated 375°F oven for 30-40 minutes, until the biscuits are browned and the filling is bubbly.
Cool for at least 10 minutes before serving. Serve hot or at room temperature.
Notes
The filling needs to cook until it's bubbly to thicken slightly.
If the biscuit topping gets too dark before the filling is bubbly, lightly tent with a piece of foil.
Mix and match the berries to your liking. You can make any combination, just try to keep the proportions the same.
If using frozen berries, don't thaw before using. Break up the frozen berries so they aren't in one large clump. Increase baking time by 10-15 minutes.