"So moist and yummy! You'd never know they were gluten-free unless I told you so! I prefer to buy my rice flour from the Asian market for the extra-fine consistency. I use a convection oven. You may need to adjust your cooking times if you do not. Cool completely before frosting or serving."
Preheat oven to 350 degrees F (175 degrees C). Grease a 13x9-inch baking dish.
Stir rice flour, soy flour, tapioca starch, cinnamon, baking soda, baking powder, nutmeg, and ginger together in a bowl.
Beat margarine in a large bowl with an electric mixer until creamy. Beat brown sugar into the margarine until incorporated and the mixture lightens in color. Add eggs one at a time, thoroughly beating each egg into the mixture before adding the next; add pumpkin and vanilla with the third egg. Gradually blend the dry mixture into the wet mixture until you have a batter; pour into the prepared baking dish.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 30 minutes.