Place butter or margarine in bowl and allow to soften. Add sugar, lemon rind, almond extract and eggs. Mix thoroughly.
Combine gluten-free flour blend and xanthan gum using a wire whisk to evenly incorporate.
Stir flour mixture into wet ingredients. Chill dough.
Roll out chilled dough 1/4-inch thick and cut with Christmas cookie cutters.
Note: This is a delicate dough, as it warms it becomes harder to handle. When this happens place the dough on a plate or piece of plastic wrap into the freezer for a few minutes to re chill, then continue on.
Combine egg white and tablespoon sugar, beat well. Brush cookies with egg white mixture and decorate with colored sugars.
Bake on parchment paper-lined cookie sheets at 350 degrees for 7 to 9 minutes watching carefully that sugar does not burn. Allow cookies to cool slightly before removing from cookie sheet.
Dough can be made one to two days in advance. Also once shapes are cut the uncooked cookies can be frozen in individual layers. Once frozen, they can be stacked. Decorating and baking can then happen on another day.