Preheat your oven to 375°F and line a 12-cup muffin tin with paper liners or grease well.
In a large bowl, whisk together 2 cups flour, sugar, baking powder, and salt.
In a separate bowl, mix the oil, eggs, milk, and vanilla until well combined.
Pour the wet ingredients into the dry ingredients and stir gently until just combined—don't overmix, mama! A few lumps are perfectly fine.
Gently fold in the blueberries, being careful not to crush them.
For the streusel topping, combine brown sugar and 1/3 cup flour in a small bowl, then cut in the cold butter with a fork until crumbly.
Divide the batter evenly among the muffin cups, filling each about 2/3 full.
Sprinkle the streusel topping generously over each muffin.
Bake for 20-22 minutes, or until a toothpick inserted in the center comes out clean and the tops are golden brown.
Let cool in the pan for 5 minutes before transferring to a wire rack. Serve warm with a pat of butter for an extra cozy treat!