Streusel-Topped Blueberry Muffins

I LOVE blueberry muffins, and I am always looking to improve on my recipe. It seems like a never-ending saga of additions and subtractions. This is my best-to-date, which I am happy to make again and again. Makes about 16-18 and no need for butter. They are already buttery!

Streusel-Topped Blueberry Muffins

Muffins:
3 cups flour
1 1/2 cups sugar
3 t baking powder
1 t salt
2 large eggs
1 cup milk
1/2 cup butter, melted
2 t vanilla
1 1/2 - 2 cups blueberries to taste

Streusel Topping:
1/4 cup (4 T) cold butter
1/4 cup flour
1/4 cup sugar

Preheat oven to 375. Line muffin tins with liners. Melt butter and set aside.
Combine all dry ingredients in large mixing bowl and stir. Combine all wet ingredients in a small bowl and blend well. Add wet ingredient mixture to dry mixture and carefully stir together. When blended well, carefully fold in blueberries. Divide into muffin cups.
Combine butter, flour and sugar into a small bowl, and using fingers, blend the ingredients together until it forms a crumbly texture. Top each muffin with equal amounts using all the topping.
Bake at 375 for about 20 minutes. Will still be light colored, but will spring back when touched. Let sit in muffin tins for 10 minutes before removing.