Preheat your oven to 400 degrees Fahrenheit.

To make the crumb topping, mix melted butter, 1 tablespoon of flour, granulated sugar, and cinnamon in a small bowl with a fork. Set this aside.

In a large bowl, whisk together the 2 cups of flour, baking powder, and salt. Set this mixture aside.

In another bowl, whisk the eggs and 1 cup of sugar together until combined. Add the vegetable oil, sour cream, and vanilla, mixing until everything is well-blended.

Pour the wet ingredients into the dry mixture and stir until just combined. Avoid over-mixing.

In a small bowl, toss 1 1/2 cups of blueberries with 1 tablespoon of flour, and gently fold this into the batter.

Fill each muffin tin about two-thirds full with the batter. Scatter the remaining blueberries on top of the muffins, and then add generous portions of the crumb topping.

Bake for 18-20 minutes, or until the muffins are lightly browned and a toothpick inserted comes out clean.

If you like, sprinkle with powdered sugar before serving.