Prep: Preheat your oven to 375°F (190°C). Line a muffin tin with baking cups or lightly grease each cup.
Mix Wet Ingredients: In a large bowl, whisk together the sugar, melted butter, oil, eggs, and vanilla until smooth. Add the milk and whisk again to combine.
Mix Dry Ingredients: In a separate bowl, whisk together the flour, baking powder, and salt.
Combine: Add the dry ingredients to the wet mixture. Stir gently with a spatula or wooden spoon just until most of the flour is incorporated. A few streaks are fine!
Prep Blueberries: Toss the blueberries with 2 teaspoons of flour to help keep them from sinking. Gently fold them into the batter.
Rest: Let the batter rest for 15 minutes to help the muffins rise tall.
Fill Muffin Cups: Divide the batter evenly among the muffin cups, filling each about ¾ full. Top with a few extra blueberries if you like.
Make Streusel: In a medium bowl, combine the melted butter, flour, sugar, and salt until crumbly. Sprinkle about 1 tablespoon of streusel over each muffin.
Bake: Bake for 22–25 minutes, until the tops are golden and a toothpick inserted in the center comes out clean.
Cool: Let muffins cool in the pan for 5–10 minutes, then transfer to a wire rack to cool completely.
Or enjoy them while still warm!