• Preheat the oven to 425 degrees Fahrenheit (220 degrees Celsius). Then line every other cup of a 12-well muffin pan with paper liners. Set aside.

Streusel

• Combine all purpose flour, white sugar, brown sugar, and melted butter in a small bowl with a fork until crumbs form. Chill in the fridge while making the muffin batter.
  40 grams all purpose flour, 40 grams granulated sugar, 20 grams brown sugar, 28 grams unsalted butter

Muffins

• Whisk all purpose flour, baking powder, salt, and cinnamon together in a large bowl. Set aside.
  280 grams all purpose flour, 1 tablespoon baking powder, ½ teaspoon salt, 1 teaspoon cinnamon
• Vigorously whisk the sugar, brown sugar melted butter, oil, eggs, and vanilla extract together in a separate bowl. Then stir in sour cream.
  200 grams granulated sugar, 50 grams brown sugar, 56 grams unsalted butter, 60 grams vegetable oil, 2 large eggs, 2 teaspoons vanilla extract, 240 grams sour cream
• Gently fold the dry ingredients into the wet ingredients with a rubber spatula. Stop when a few white streaks of flour are left.
• Toss the frozen blueberries with 1 tablespoon of flour and gently fold them into the batter until the dry streaks just disappear.
  220 grams frozen blueberries
• Use an ice cream scoop to fill each paper liner to the top with batter and sprinkle with streusel.
• Bake at 425°F for 5 minutes. Reduce the heat to 350°F (180°C) and bake for 14-16 minutes or until a toothpick inserted in the center of a muffin comes out clean with a few moist crumbs attached.
• Remove from the oven and let the muffins cool in the hot pan for 5-10 minutes. Transfer to a wire rack to cool completely for about 1 hour.
• Reline the pan with liners and bake the rest of the muffin batter. Don’t forget to increase the oven temperature again before baking!