In a medium bowl, mix together the margarine, brown sugar, white sugar and egg until smooth. Stir in the peanut butter and cashew butter. Combine the baking soda, corn flour, tapioca flour, and potato flour; stir into the batter to form a dough. Roll the dough into teaspoon sized balls and place them 2 inches apart onto an ungreased cookie sheet.
Bake for 8 to 10 minutes in the preheated oven. Let cool on baking sheets for a few minutes before removing to wire racks to cool completely.