• Preheat the oven to 350°F
• Line the muffin tin with paper liners or grease the cups with butter.
• Combine almond flour, all-purpose flour, sugar, baking powder, salt, and lemon zest in a bowl.
• Combine the melted butter, sour cream, eggs, and vanilla extract separately. Mix until well combined.
• Gently pour the wet mixture into the dry ingredients.
•  Fold the ingredients together using a spatula, careful not to over-mix. The batter may be lumpy, but that's okay.
• Toss the fresh blueberries with 1- tablespoon of flour. This will help prevent the blueberries from sinking to the bottom of the muffins. 
• Gently fold the floured blueberries into the batter.
• Add lemon juice to the batter and gently fold it in. The lemon juice will add flavor and a touch of acidity to balance the sweetness.
• Fill each muffin cup about two-thirds with the batter using an ice cream scoop.

 Streusel Topping:

• Combine the flour, sugar, softened butter, and lemon zest for the streusel topping.
• Use your fingers to crumble the ingredients together until they resemble coarse crumbs.
• Sprinkle streusel topping over each muffin evenly.
• Bake for about 15-20 minutes or until a toothpick inserted comes out clean.
• Once baked, remove the muffins from the oven and let them cool for about 5 minutes before serving.