Make the crumb topping:
In a small bowl, combine granulated sugar, flour, butter and cinnamon. Press butter into dry ingredients with a fork until all ingredients are incorporated. Mixture will be lumpy. Set aside.
Make the muffins:
Preheat oven to 375F degrees. Butter muffin cups or line with muffin liners.
In a medium bowl, combine the flour, sugar, salt and baking powder. Set aside.
In a small bowl, combine the oil, egg and buttermilk. Whisk to incorporate.
Stir liquid mixture into dry ingredients and stir just to combine. You will have a lot of flour that is still visible. This is okay.
Sprinkle 1 teaspoon flour over the blueberries and toss to coat. Gently fold blueberries into batter.
Fill muffin tins 3/4 full.
Sprinkle desired amount of crumb topping over each muffin (less is more here).
Bake for 20 to 25 minutes, or until tops are golden. Do not overbake.
Remove from oven and let cool at least 10 minutes on cooling rack before serving.
Note: This recipe makes 6 large muffins or 12 regular size muffins. The crumb topping adds a nice delicate crunch but for best results, don't add too much. If you add too much topping, the muffin tops may burn. A good amount is about 1 teaspoon topping per muffin.