Preheat oven to 400 degrees. Grease the top of a 12-muffin muffin pan. Place baking cups in 8 of the muffin wells. Put a tablespoon of water in the remaining empty wells.
Make the topping: With a fork, mash together ¼ cup sugar, 2 tablespoons all-purpose flour, and all of the butter and cinnamon in a bowl until the mixture has a coarse, sand-like, crumbly texture. Set aside.
Stir together the 1 ½ cups flour, ¾ cup sugar, salt, and baking powder.
In a medium to large measuring cup, add ⅓ cup vegetable oil and 1 egg. Add milk to the oil and the egg until the total volume reaches 1 cup. In the measuring cup, stir the oil, egg, and milk together to combine.
Stir the liquid mixture into the flour mixture until JUST combined. It will still be lumpy, and it's totally okay if you can still see streaks of flour in the mix.
Gently fold in the blueberries.
Fill the 8 prepped muffin cups in the muffin tin right up to the top. Sprinkle a heaping teaspoon of the topping over each batter-filled cup.
Bake for 22 minutes. Serve warm or room temperature.