Preheat the Oven: Set your oven to 400°F (200°C). Line a muffin pan with paper liners, or grease each cup if you prefer not to use liners.
Prepare the Dry Ingredients: In a medium bowl, whisk together 1 ½ cups flour, ¾ cup sugar, ½ teaspoon salt, and 2 teaspoons baking powder until well combined.
Prepare the Wet Ingredients: In a separate bowl or measuring cup, whisk together ⅓ cup vegetable oil, 1 egg, and ⅓ cup milk until smooth.
Combine Wet and Dry Mixtures: Gently fold the wet ingredients into the dry ingredients using a rubber spatula, mixing just until a few streaks of flour remain.
Add Blueberries: Fold in the blueberries, being careful not to overmix.
Make the Crumble Topping: In a small bowl, mix together ½ cup flour, ½ cup sugar, ¼ cup cubed butter, and 1 ½ teaspoons ground cinnamon. Use a fork to break up the butter until the mixture forms coarse crumbs.
Fill the Muffin Pan: Spoon the muffin batter into the prepared muffin cups, filling each one to the top. Generously sprinkle the crumble topping over each muffin.
Bake: Bake in the preheated oven for 20-25 minutes or until a toothpick inserted into the center of a muffin comes out clean.
Cool and Enjoy: Allow muffins to cool in the pan for a few minutes before transferring them to a wire rack to finish cooling. Enjoy warm or at room temperature!
