Preheat oven to 350°F (175°C). Grease and flour a 9x13-inch baking pan. Prepare cake according to package directions using eggs, oil, and water, then bake for 28-32 minutes until a toothpick comes out clean. Let cool completely in the pan.

While cake cools, make the buttercream by beating softened butter in a large bowl until fluffy, about 2 minutes. Gradually add powdered sugar, then mix in heavy cream and vanilla extract until smooth and creamy.

Crumble the cooled cake into a large mixing bowl using your hands until it resembles fine crumbs with no large chunks remaining. Add 3/4 cup of the buttercream and mix with your hands or a wooden spoon until the mixture holds together when squeezed but isn't overly wet.

Roll the mixture into 1.5-inch balls (about 1.5 tablespoons each) and place them on a parchment-lined baking sheet. You should get approximately 48 cake balls.

Refrigerate the cake balls for at least 2 hours or freeze for 30 minutes until very firm. This step is crucial for successful dipping.

Melt candy coating in a microwave-safe bowl in 30-second intervals, stirring between each, until completely smooth. If coating is too thick, stir in 1 teaspoon vegetable shortening.

Remove a few cake balls from the refrigerator at a time. Dip the tip of a lollipop stick into the melted coating, then insert it halfway into a cake ball. This helps the cake pop stay secure.

Dip each cake ball into the melted coating, fully submerging it. Lift it out and gently tap the stick against the side of the bowl to remove excess coating and create a smooth finish.

While the coating is still wet, add sprinkles if desired. Stand the cake pop upright in a styrofoam block or lay flat on parchment paper to set.

Let the coating harden completely at room temperature for about 30 minutes before serving or packaging. The coating should be firm to the touch and no longer glossy.