Before starting, pre-heat oven to 400 degrees F. After greasing muffin tins, blend together melted butter, lemon juice and maple syrup in mixing bowl. Add zest and mix in lightly beaten eggs. In separate bowl, sift flour, baking powder, sugar and salt. After combining both mixtures, spoon mixture evenly into muffin tins. Lightly sprinkle tops with the two teaspoons of sugar. Bake for 20 to 25 minutes, or until toothpick inserted in centers comes out clean.