Preheat oven to 375*. Grease muffin pan or line with paper liners.
In a medium bowl, combine flour, 1 cup of the sugar and baking powder.
In a large bowl, whisk together eggs, milk, butter, lemon zest and lemon juice. Stir in flour mixture, mixing just until combined. Fold in the chocolate chips. Do not overmix.
Scoop batter into prepared muffin cups. Sprinkle remaining sugar evenly over tops.
Bake in preheated oven for 20 to 24 minutes or until puffed, light golden and a skewer inserted into center comes out clean. Let cool in pan on rack for 5 minutes. Remove from pan and let cool completely on rack.