Low Fat Blueberry Muffins

Name: Low Fat Blueberry Muffins
Prep time: 10 min
Cook time: 25 min
Total time: 35 min
Cuisine: American
Ingredients: 150 grams plain/all purpose flour (1 and 1/8 cup); 1 tablespoon baking powder; 1/2 teaspoon salt; 50 grams low-fat butter - melted (1/4 cup); 1 large egg; 100 millilitres non-fat milk (6 and 1/2 tablespoons); 30 grams sugar (2 and 1/2 tablespoons); 1 teaspoon vanilla extract; 1 lemon - zest of whole and juice of half of it; 200 grams blueberries; 1 tablespoon demerara/turbinado sugar