Preheat the oven to 350?. Grease or line a cookie sheet with parchment paper.
In a microwave-safe medium-large mixing bowl, heat the butter just until melted. I let the butter sit at room temperature for a few minutes. You don’t want it to be hot when mixing the ingredients together. Add the eggs and vanilla extract to the melted butter and whisk the ingredients together until combined.
Add ½ of the cake mix to the wet ingredients. Stir together just until incorporated (you don’t want to overmix the dough)
Add the remaining cake mix and stir together until incorporated.
Add ¼ cup of the jimmies to the dough and fold them in until they are distributed throughout the dough.
Place the cookie dough in the fridge for about 5 minutes. This is an optional step, however, the dough will be really thick and sticky and this makes it much easier to work with.
Pour the remaining ¼ cup of jimmies into a small bowl.
Using a medium cookie scoop, scoop the dough and roll into uniform balls. Dip the top of each dough ball into the bowl of jimmies to coat the tops in sprinkles. Place the cookie dough balls at least 1.5” apart from each other on the prepared cookie sheet.
Bake the cookies for 8-11 minutes or until they are cooked through.
Let the cookies set up for about 3-5 minutes on the baking pan before attempting to move them to a cooling rack.