In a large bowl, mix dry ingredients: flour, soda, salt, and cinnamon. Set aside. In a separate bowl, whisk the eggs, oil, sour cream, vanilla and sugar. Add to dry ingredients and stir just until moist. Gently stir in blueberries.
To make streusel topping, combine butter, sugar, flour, and cinnamon in a mixing bowl and press with a fork to mix. Add oats, and mix until coarse crumbs form.
Fill greased or paper lined muffin pans 3/4 full of batter. Sprinkle about 2 teaspoons full of streusel
topping on each muffin,
Bake in a pre-heated 400 degree oven for 20-23 minutes, until done. Cool in pan 5 minutes and then cool on wire racks.
* If lining muffin cups with paper liners, this recipe will make 15 or so muffins. Directly to the pan it
makes a full dozen. These muffins remove very easily from a greased muffin pan, if you cool for 5
minutes in the pan. The blueberries give the batter a purple hue as well.