Preheat the oven to 375 degrees F. Butter a 2-quart shallow baking dish or eight 6-ounce ramekins (if you are using ramekins, double the filling).
Make the topping: Whisk the cornmeal, flour, brown sugar and salt in a bowl. Stir in the almonds. Work in the butter with your fingers until evenly moistened.
Make the filling: Toss the blueberries, granulated sugar, flour and lemon juice in a bowl.
Transfer the filling to the prepared dish or ramekins and dot with 2 tablespoons butter. Squeeze handfuls of the crumble mixture and scatter on top of the fruit. Bake until golden and bubbly, 40 to 45 minutes.
Let sit 10 minutes before serving. Top with whipped cream or ice cream, if desired.