In a large bowl, beat eggs and milk well, with a whisk. Add the flour, melted butter, sugar, salt and xanthan gum (if using). Whisk again, very well until there are no lumps and the batter is the consistency of heavy cream.
(If using gluten free flour and xanthan gum, let the batter rest for about 10 minutes, in order to thicken.)
Heat a 9" pan over medium heat. With a pastry brush, brush a little melted butter on the surface of the pan. Fill a ladle with batter. Lift the pan away from the heat, and slowly pour the batter into the pan, while tilting and rotating the pan slowly. Once the batter has evenly coated the bottom of the pan, place back on heat and cook for about 1 minute, or until the batter has dried. Using a large spatula, flip the crepe over. Cook on the second side for about 1 more minute, or until a very slight amount of very light brown appears on parts of the crepe. Remove to a plate and cover with a kitchen towel while preparing the rest.
Fill with your choice of fillings, roll up as you would a burrito, and enjoy!