Blueberry Muffins

1 ¾ cups plus 1 T flour, divided
2 ¾ tsp baking powder
¾ tsp salt
½ cup plus 1 T sugar, divided
2 tsp orange or lemon zest
1 large egg
¾ cup buttermilk
1/3 cup oil
1 cup fresh or frozen blueberries

Streusel Topping
¼ cup sugar
2 ½ T flour
½ tsp cinnamon
1 ½ T butter

Preheat oven to 400°.  Line a 12-cup muffin tin with cupcake liners and set aside.
Lightly spoon 1 ¾ cups flour into measuring cups and level with a knife.  Combine flour with baking powder, salt, ½ cup sugar, and citrus zest in a large bowl.  Make a well in the center of the mixture.  Whisk together the egg, buttermilk, and oil in a separate small bowl.  Add to dry ingredients, stirring just until moistened.
Combine remaining 1 T flour and 1 T sugar in a small bowl and then toss blueberries into this mixture until they are well coated.  Gently fold blueberry mixture into the batter.  Spoon batter into lined muffin tins, filling 2/3 full.

For the Streusel topping:  Combine sugar, flour, and cinnamon.  Cut in butter with a pastry cutter or 2 butter knives until the mixture is crumbly.  Sprinkle over batter and bake 18 minutes or until tops are golden and a toothpick inserted into the center of a muffin comes out clean.  Remove from oven and allow to cool in the pan for 5 minutes.  Transfer to a cooling rack.