• Preheat oven to 400°F. Set the oven rack to the middle. Grease 12 muffin tins or line with paper liners. I am using a standard 12-cavity non-stick muffin pan.

For the Streusel:

• Whisk together the sugar, flour, and melted butter in a small bowl. Use your hands or a fork to mix until it’s clumpy. Set aside in the refrigerator until you are ready to use.
  ¼ cup salted butter, ⅔ cup all-purpose flour, ⅓ cup brown sugar

For the Muffins:

• You can either use a hand blender, a standard blender, or a hand whisk to mix the wet ingredients.
• In the bowl of a standard blender, add cottage cheese, melted butter, eggs, sugar, and vanilla extract. Mix on high for a minute or until completely smooth.
  1 cup cottage cheese, ½ cup salted butter, 2 large eggs, ⅓ cup Granulated sugar, ½ cup dark brown sugar, ½ tablespoon vanilla extract
• Whisk together the dry ingredients in a medium bowl.
  2 cups all-purpose flour, 2 teaspoons baking powder, ¾ teaspoon baking soda, ½ teaspoon allspice
• Gently add the cottage cheese mixture to the bowl of flour in two batches, mixing with a rubber spatula just until combined. Avoid overmixing to keep the muffins tender.
• Using the same spatula, carefully scrape down the sides of the blender to get out all the mixture. If needed, add about a tablespoon of milk to the blender, swirl it around, and pour it into the batter so nothing goes to waste.
• If you prefer, toss the blueberries with about ½ tablespoon of all-purpose flour before folding them into the batter. This light coating helps prevent them from sinking to the bottom as they bake.
• Add the blueberries to the batter and fold until combined.
  1 ½ cups fresh blueberries
• Using a cookie scoop or measuring cup, fill each muffin liner about ¾ full. If there’s any batter left, divide it evenly among the liners so they bake up uniformly.
• Sprinkle the crumble topping evenly over each muffin (if using).
• Transfer into the preheated oven. Bake at 400°F for 12 minutes, then reduce the temperature to 350°F and bake for 13-15 minutes, or until a toothpick inserted into the center of the muffins comes out clean.
• Let the muffins rest for 5-10 minutes after baking to set the crumb. Serve warm or at room temperature.

  (Please see the body of the post for serving options, substitutions, step-by-step photos, and recipe FAQS to answer any questions.)