For the pastry, cream together first measure of margarine and cream cheese substitute. Mix together the garbfava flour, sorghum flour, corn starch, tapioca starch and xanthan gum. Add the flours to the creamed mixture and blend until thoroughly combined. Chill in a covered container for at least one hour.
To make tassies: When ready to bake, preheat oven to 325 degrees F. Make the filling by combining the brown sugar, second measure of margarine and egg until blended. Stir in pecans. Press a rounded teaspoon of pastry dough on the bottom and sides of 24 mini muffin cups. Fill each pastry with 1 heaping teaspoon of pecan filling.
Bake at 325 degrees F for about 30 minutes until pastry is golden and filling is set (it should be puffed). Allow to cool for five minutes then carefully remove tassies from pan using a thin sharp paring knife, if needed. Allow to cool completely on a cooling rack.