Important! About an hour before you’re ready to bake, set all refrigerator items out on the counter to bring them to room temperature. (If you live in a warm environmennt, this may take much less time.)
Preheat the oven to 425°F. Line a 12 cup muffin pan with paper liners or coat with nonstick spray. (Alternatively, use a Texas muffin pan to make 6 giant sized muffins.) Set aside.
For the crumble topping, combine sugars, cinnamon, and salt in a medium bowl. Whisk in the melted butter. Add flour. Stir just until moistened. Spread the mixture onto parchment paper to dry until ready to use.
For the muffins, whisk dry ingredients together in a large bowl. Set aside.
Whisk the melted butter, oil, sugar, and eggs together until combined. Whisk in the sour cream, milk, and vanilla extract. Pour wet ingredients into dry ingredients and fold together until completely combined. Avoid over mixing. Batter should be thick enough to spoon. Fold in the blueberries.
Use a ¼ - ½ cup measuring cup to scoop batter into muffin cups. Fill all the way to the top! Don’t be afraid!
Sprinkle the reserved crumb topping on top. Use your fingers to gently press the crumbs into the batter. The more crumb topping, the better! Optionally, sprinkle with coarse sugar for a bit of added crunch.
Bake at 425°F for 5 minutes. With the muffins remaining in the oven, reduce the temperature to 350°F and continue to bake for another 25-35 minutes or until a toothpick pressed into the center comes out clean. Tops should be lightly golden brown.
Allow to cool in the pan for 10 minutes before serving.