Bake cake in a 9 by 13-inch pan following the package directions. Let cool, then remove from pan and add to a very large bowl (it’s ok if you need to break the cake into pieces). Set the bowl in the fridge to chill for about 15 minutes while you prepare the buttercream.
Line a large sheet pan with parchment paper. Remove the cake from the fridge and using your hands, break the cake up into very small crumbs. You want the texture to resemble coarse sand. Add the buttercream and mix until it is evenly incorporated. The cake should resemble cookie dough. Using a 1.5-tablespoon sized cookie scoop, portion the cake mixture into even balls and set on the prepared baking sheet.
Once you have made even portions, use your hands to roll each one into a smooth, even ball. Set on prepared baking sheet and place in the freezer for 30 minutes.
While the cake chills, set up a decorating rack where the cake pops can safely set after they are dipped in chocolate. A block of styrofoam, or an old box with holes the same size as the lollipop sticks punched into it works well.
When the cake has about 5 minutes left of freezer time, prepare the white chocolate coating. Add white chocolate melts and coconut oil to a large microwave safe measuring cup. Melt in the microwave using 30 second increments until completely smooth. Mix well to incorporate the coconut oil into the chocolate.
Remove the cake from the freezer. Dip about ½ inch of the stick in the melted chocolate, then set it into the chilled cake balls to help it set securely in place. Chill again for 10 minutes to allow the sticks to set.
Working with one pop at a time, dip the cake into the melted chocolate, stirring to evenly coat. Take care to let all of the excess chocolate dip off of the cake pop, tapping it on the side of the measuring cup as needed. Once it is no longer dripping with chocolate, set it securely in the decorating rack. Working quickly, add desired sprinkles on the top of the pop before the coating sets.
Repeat with remaining cake pops. The coating should set at room temperature within 5 minutes.