Preheat the oven to 350°. Lightly grease two 8-inch round baking pans with cooking spray.
Prepare the cake mix using the butter, oil, eggs, and milk as directed on the box.
Bake in the prepared pans until golden brown and a toothpick inserted into the middle comes out clean, about 22-26 minutes. Do not overbake, or the cake will be dry.
Immediately after removing from the oven, transfer the hot cake to the bowl of a stand mixer fitted with the paddle attachment. Mix on medium speed until the cake crumbles. Let the cake mixture sit to cool slightly while you make the buttercream (you still want it to be somewhat warm when you shape the cake pops.)
For the buttercream: In medium bowl using a hand mixer, beat the butter on medium-high speed until creamy, about 1 minutes. Add the powdered sugar along with the cream/milk, vanilla and salt. Mix on low speed for 30 seconds, then increase to medium-high speed and whip for another minute.
Add the buttercream to the cake crumbs and continue mixing until the mixture is moist and holds together, about 2 minutes.
While the cake mixture is still warm, scoop about 2 tablespoons at a time and roll into balls between your hands, then place on a parchment-lined baking sheet.
Place in the freezer until firm, about 15 minutes.
Melt the candy melts a microwave-safe bowl, stirring every 30 seconds until smooth.
Remove the cake balls from the fridge. Dip the tip of each cake pop stick into the melted chocolate, then insert into the center of a cake ball. Dip the entire cake pop into the melted chocolate, lifting and twisting gently until the dripping slows. Immediately decorate with sprinkles. Place upright in a cake pop stand.
Allow the cake pops to completely set before serving.