In a large mixing bowl, stir together the cake mix, oil, eggs, and sour cream until fully combined.
Use a cookie dough scoop or tablespoon to drop the cookie dough in mounds onto a baking sheet lined with parchment paper. (We made 2 tablespoon size cookies.)
Bake cookies for 11 minutes, until puffed and set.
Allow cookies to cool for 1-2 minutes and then transfer to a cooling rack to cool completely.
Make the frosting by beating together the butter and cream cheese until smooth. Beat in the powdered sugar, one cup at a time. Add in the vanilla extract. Frosting will be softer than a cake frosting.
Spread a generous layer of frosting over each cooled cookie and top with a sprinkle of chopped walnuts.
Notes
Storage:Store cookies in a single layer in an airtight container in the refrigerator for 4-5 days or freeze for up to 3 months.Notes:Cookies are super moist and chewy. They stay soft and fresh for days.The recipe makes ample frosting. You can probably halve the frosting recipe for a bit lighter layer on the cookies.1 - 1 ½ tablespoon scoops of cookie dough will bake in 8 minutes.We did not find any difference in using chilled dough or baking it right out of the mixing bowl. If you would like to make the dough in advance, cover it with plastic wrap and store it in the refrigerator up to a day in advance.