Preheat your oven to 400°F (200°C). Grease 8 muffin cups or line them with paper liners. Gather all your ingredients, ensuring everything is ready and within reach before you start mixing.

In a large bowl, whisk together 1 1/2 cups of all-purpose flour, 3/4 cup granulated sugar, 2 teaspoons baking powder, and 1/2 teaspoon salt until thoroughly combined.

Pour 1/3 cup vegetable oil into a liquid measuring cup. Add 1 large egg and then add enough milk to reach the 1-cup mark (using about 1/3 cup milk, or slightly more if needed). Stir until the wet ingredients are blended. Pour this mixture into the bowl of dry ingredients and mix just until everything is combined—don't overmix. Gently fold in 1 cup of fresh blueberries. Set the batter aside.

In a small bowl, combine 1/2 cup granulated sugar, 1/3 cup all-purpose flour, 1/4 cup unsalted butter (in cubes), and 1 1/2 teaspoons ground cinnamon. Use a fork to mix everything together until the mixture becomes crumbly. I like to make sure there are some bigger crumbs for extra texture on top of the muffins.

Divide the muffin batter (from Step 3) evenly among the prepared muffin cups, filling each right to the top. Sprinkle the crumb topping (from Step 4) generously over each muffin.

Bake the muffins in the preheated oven for 20 to 25 minutes, or until a toothpick inserted into the center of a muffin comes out clean. Allow them to cool slightly before enjoying. For an extra touch, I sometimes let the muffins cool in the pan for about 5 minutes before transferring them to a wire rack, which helps the crumb topping set nicely.