This is the best one I've found, and it's pretty dang close to the real thing!
1 (19 oz.) box French vanilla cake mix
1/3 C. vegetable oil
1/2 C. unsalted butter, softened
3-5 C. powdered sugar
1/2 C. milk
2 tsp. vanilla extract
food coloring, if desired
1. Preheat oven to 350. Blend cake mix, eggs and oil until moistened. Roll into 1" balls. Place on ungreased cookie sheet. Flatten with a glass (but not too much. You want them to be 'fluffy').
2. Bake for 6-8 minutes. Cool 1 minute on pan before moving to a cooling rack.
3. Frosting: Place butter in large bowl. Add 4 cups sugar and then milk and vanilla. Beat on medium speed until smooth and creamy, approx. 3-5 minutes. Gradually add remaining sugar, 1 cup at a time, beating well after each addition, about 2 minutes, until the icing is thick enough to spread. Add food coloring if you like.
4. While the cookies are still a little warm, spread on some buttercream frosting. Allow the frosting to set up before storing.
Confession: I didn't actually beat it for 3-5 minutes, and then 2 minutes after each cup of sugar. Which might be why I ended up adding an extra cup of sugar because it seemed too thin. The result was some really yummy frosting that could have been a little less sweet.