For the muffins: Line a 12-cup muffin tin with foil muffin cup liners.
Toss the berries with 2 tablespoons of the flour in a small bowl. Whisk the remaining flour, granulated sugar, baking powder and salt in a large bowl. Beat the eggs in a medium bowl until frothy, and then whisk in the milk, melted butter and vanilla. Make a well in the dry ingredients and pour the wet ingredients into the well. Stir the batter with a rubber spatula until just combined.
For the topping: Combine the flour and brown sugar in a medium bowl. Either using a fork or your fingers, mix in the butter to form large and medium crumbs.
Scoop the batter into the muffin cups, filling just above three-quarters full. Divide the blueberries among the cups. Divide the topping among the muffins, pressing lightly. Freeze until set, about 3 hours. The muffins can be removed to zippered freezer bags at this point and stored for up to 2 months.
When ready to bake, preheat the oven to 325 degrees F. Place the muffins in a muffin tin or directly on a baking sheet and bake until they are lightly golden and a tester inserted in the center comes out clean, 35 to 40 minutes.
These muffins can also be baked immediately. Preheat the oven to 350 degrees F, and bake until lightly golden and a tester inserted in the center comes out clean, 20 to 25 minutes.