Gluten Free Sugar Cookies II

I figured out how to make gluten free sugar cookies with some minor modifications. Made the above cookies today 12/20/11

1 1/2 cups brown rice flour
2/3 cup cornstarch (can also use arrowroot powder)
1/3 cup tapioca starch/flour
1 1/2 cups powdered/confectioner's sugar
1 tsp xanthan gum
1 tsp baking soda
1 tsp cream of tartar
3/4 cup cubed cold butter
1 egg
1 tsp vanilla extract

1. Combine all the dry ingredients in a bowl and mix together. Place in a large food processor and using a metal blade, pulse about 3-4 times
2. Cut up the butter into sliced or cubes and add to the food processor and pulse about 10 times.
3. Add the egg and vanilla extract and pulse until the mixture forms a ball
4. Place the dough in a covered container and place in the fridge for at least 3 hours
5. Roll dough between parchment paper to about 1/4-1/2 inch thick then cut out your shapes.
6. Place on a cookie sheet and put in the fridge for about 10-20 minutes before baking. If the cookies get too soft they will not hold their shape while baking
6. Bake 6-8 minutes at 350, until lightly browned.

update 12/20: the thicker the cookie the softer it is. I left the dough in the fridge overnight so I had to let it soften a little before rolling out, then put the shapes back in the fridge before baking.

I modified from this original recipe: http://glutenfreecooking.about.com/od/seasonalandholiday/r/gfsugarcookies.htm
I followed this recipe in the beginning using vanilla extract instead of the lemon extract and omitting the lemon peel. They were too greasy and buttery when baked and burned too easily. I also could not make shapes as they flattened in the oven. I looked at other sugar cookie recipes that called for a cup of butter but had more of a flour ratio than this recipe.