Preheat your oven to 375°F (190°C) and line muffin tins with baking cups or spray with cooking oil.

In a large bowl, whisk together the sugar, melted butter, vegetable oil, eggs, and vanilla until smooth. Add the milk and whisk until well combined.

In another bowl, whisk together the flour, baking powder, and salt. Gently fold the dry ingredients into the wet mixture until just moistened.

Toss the blueberries with 2 teaspoons of flour to coat, then gently fold into the batter. Let the batter rest for 15 minutes.

Fill muffin cups about ¾ full and top with extra blueberries and the streusel mixture.

To prepare the streusel, mix melted butter, flour, sugar, and salt in a medium bowl. Sprinkle this mixture over the muffins.

Bake for 22-25 minutes, or until golden and a toothpick comes out clean. Cool for 5-10 minutes before transferring to a wire rack.