How to Make It
Preheat oven to 350°F. Beat cake mix, milk, melted butter, and 1 teaspoon of the vanilla in bowl of a heavy-duty stand mixer fitted with paddle attachment on low speed until well blended, about 1 minute. Increase speed to medium, and beat 2 minutes. Pour batter into a greased (with vegetable shortening) and floured 13- x 9-inch baking pan.
Bake in preheated oven until a wooden pick inserted in center comes out clean, 24 to 28 minutes. Cool in pan on a wire rack 15 minutes. Turn cake out onto wire rack, and let cool completely, about 2 hours.
Meanwhile, beat cream cheese and softened butter with heavy-duty stand mixer fitted paddle attachment on medium speed until creamy. Reduce speed to low, and gradually add powdered sugar and remaining 2 teaspoons vanilla, beating until blended. Increase speed to medium-high, and beat until fluffy, 1 to 2 minutes.
Crumble cooled cake into a large bowl. Stir in 2 cups of cream cheese frosting. (Reserve any remaining frosting for another use.) Roll cake mixture into 48 balls, about 1-inch in diameter. Place balls on baking sheets, and cover with plastic wrap. Chill 8 hours or overnight.
Melt 1 package of the melting wafers in a medium-size microwavable bowl in microwave according to package directions. Start with 16 cake balls (continue to chill remaining 32 cake balls). Using a fork and working with 1 cake ball at a time, dip ball into melted wafers, allowing excess to drip back into bowl. Place ball on a parchment paper-lined baking sheet, and immediately sprinkle with desired amount of sprinkles or sanding sugars. Repeat with remaining 15 cake balls and melted wafers in bowl, cleaning fork between each dip. Wipe bowl clean, and repeat 2 more times with remaining chilled cake balls and 2 packages of melting wafers, and desired amount of sprinkles. Chill until ready to serve.