Preheat oven to 375, rack in the middle position.
Grease the bottoms only of a 12-cup muffin pan (or line the cups with cupcake papers.) Melt the butter. Mix in the sugar. Then add the beaten eggs, baking powder and salt and mix thoroughly.
Put one Tablespoon of the flour in a plastic bag with your cup of fresh or frozen blueberries. Shake it gently to coat the blueberries and leave them in the bag for now.
Add half the remaining two cups flour to your bowl and mix it in with half the milk. Then add the rest of the flour and milk and mix thoroughly.
Here comes the fun part: Add 1/2 cup blueberry pie filling to your bowl and mix it in. (Your dough will turn a shade of blue but don’t let that stop you—once the muffins are baked they’ll look just fine.) When your dough is thoroughly mixed, fold in the flour-coated fresh or frozen blueberries.
Fill the muffin tins three-quarters full and set them aside. If you have dough left over, grease the bottom of a small tea-bread loaf pan and fill it with your remaining dough.
The crumb topping: Mix the sugar and the flour in a small bowl. Add the softened butter and cut it in until it’s crumbly. (You can also do this in a food processor with hard butter using the steel blade.)
Sprinkle the crumb topping over your muffins and bake them in a 375F oven for 25 to 30 minutes. (The tea-bread should bake about 10 minutes longer than the muffins.)
While your muffins are baking, divide the rest of your blueberry pie filling into 1/2-cup portions and pop it in the freezer. Use paper cups to hold it and freeze them inside a freezer bag. All you have to do is thaw a cup the next time you want to make another batch of muffins.
When your muffins are baked set the muffin pan on a wire rack to cool for at least 30 minutes. (The muffins need to cool in the pan for easy removal.) Then just tip them out of the cups and enjoy.