1. 1. Prepare Your Muffin Tin: Start by preheating your oven to 375 F (190 C). Line a 12-cup muffin tin with paper liners or grease it thoroughly with non-stick spray. This prevents sticking and makes for easy cleanup.

2. 2. Combine Dry Ingredients: In a large mixing bowl, whisk together the 1 1/2 cups all-purpose flour, 1/2 cup granulated sugar, baking powder, and salt. Make sure there are no lumps and everything is well combined.

3. 3. Mix Wet Ingredients: In a separate medium bowl, lightly beat the large egg. Then, stir in the milk, vegetable oil, and vanilla extract until they are fully incorporated.

4. 4. Combine Wet and Dry Mixtures: Pour the wet ingredients into the bowl with the dry ingredients. Stir gently with a spatula or wooden spoon until just combined. Be careful not to overmix; a few lumps are perfectly fine. Overmixing can lead to tough muffins.

5. 5. Fold in Blueberries: Gently fold in the fresh blueberries. Try to distribute them evenly throughout the batter without crushing them too much.

6. 6. Prepare the Streusel Topping: In a small bowl, combine the 1/4 cup all-purpose flour and 2 tablespoons granulated sugar for the streusel. Add the cold, cubed butter and use your fingertips or a pastry blender to cut the butter into the flour mixture until it resembles coarse crumbs.

7. 7. Fill Muffin Cups and Top: Divide the muffin batter evenly among the 12 prepared muffin cups, filling each about two-thirds full. Sprinkle a generous amount of the streusel topping over the batter in each cup.

8. 8. Bake to Golden Perfection: Bake for 20-25 minutes, or until the tops are golden brown and a wooden skewer or toothpick inserted into the center of a muffin comes out clean. Let the muffins cool in the tin for a few minutes before transferring them to a wire rack to cool completely.