In a large mixing bowl, stir together the cake mix, oil, eggs, and sour cream until fully combined. Fold in rainbow jimmies until evenly distributed.
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.
Notes
We made 2 Tablespoon sized cookies, if you make them smaller they will likely need less time in the oven.
You'll need a standard 15.25 ounce box of funfetti cake mix, the kind that uses vegetable oil, eggs, and water. However, you will not need the water for these cookies. Please follow the ingredients we have provided in the recipe card as you'll be using sour cream in addition to the vegetable oil and eggs.
Rainbow jimmies are the best kind of sprinkle to use as they don't tend to bleed their color when met with wet batter.
Store cookies in an air-tight container kept at room temperature for 4-5 days.
To freeze the dough, place the dough balls on a baking sheet and flash freeze until solid. Transfer the solid dough balls to a large ziptop bag and freeze for up to 3 months. To freeze baked cake mix cookies, store in a large ziptop bag or air-tight container kept in the freezer for 2-3 months. Thaw at room temperature.
You can prepare the cookie dough, cover it with plastic wrap, and store it in the refrigerator up to a day in advance. You can even shape the dough into balls so they are ready to pop into the oven when you’re ready.