I haven't had a sugar cookie in years - mostly because even before I had to go gluten free, I was just too darn lazy to go to the trouble of rolling out the dough, cutting it out with those cute little cookie cutters, and so forth.
I like the idea of a sugar cookie that I can mush up in my hands and stick on the baking sheet. This is that kind of sugar cookie. And it's crisp on the outside, and soft and cakey on the inside -- because it's made with CAKE.
Gluten Free Sugar Cookies

2 eggs
1/4 C butter, melted
1 tsp vanilla
Decorative sugars
Preheat your oven to 375. Combine the cake mix, the eggs, the butter and the vanilla together, blending well until you've got dough - and yes, it will look a little crumbly, but that's ok.
Roll the dough into balls, about 1" across (that gives you two dozen cookies), and place on a baking sheet. I like to line mine with parchment paper, because I'm a fan of working smarter and not harder, and it makes it way easier to clean up. Use the bottom of a glass to press down the dough balls, and then sprinkle with the decorative sugars. Bake for about 12 minutes, or until the edges begin to turn golden.
Seriously, you guys, these are fabulous!