1Combine dry muffin ingredients in large bowl; add blueberries & toss gently. Set aside.
2Combine together: buttermilk, oil, and slightly beaten egg; add to dry ingredients, stirring until dry ingredients are moistened. Note: dough will be stiff.
3Spoon batter into muffin tins coated with cooking spray. (I line muffin tins with paper cupcake holders) Fill 2/3 full.
Toss together streusel ingredients (margarine should be room temperature or can be melted first) Sprinkle evenly on top of muffin mixture prior to baking.
Bake at 400 degrees for 15-20 minutes.