Preheat oven to 400 degrees Fahrenheit (200 degrees C). Grease muffin pan or line with muffin liners.
In a large bowl, combine 2 ¼ c flour, 1 c sugar, salt, and baking powder. Mix well.
Add the oil, egg, and milk to the flour mixture. Stir until combined.
Gently fold in blueberries.
Fill muffin cups to the top.
Make the Streusel Topping: Add ¾ c sugar, ½ c flour, ¼ c cold, cubed butter, and ½ Tbsp ground cinnamon to a medium bowl. Use a pastry cutter to blend the ingredients together.
Generously sprinkle to topping over the muffins before baking.
Bake for 20- 25 minutes until an inserted toothpick comes out clean.