Preheat oven to 350°F (175°C) and prepare a muffin tin.
Whisk together flour, baking powder, and salt.
Beat egg, then stir in cottage cheese, Greek yogurt, lemon zest, lemon juice, sugar, and melted butter.
Fold dry ingredients into wet until just combined.
Divide batter into muffin cups and top with optional crumb topping.
Bake for 18–22 minutes, until a toothpick comes out clean.
