1Heat oven to 350°F. Spray bottom of 13x9- inch pan with cooking spray. Make and bake cake mix in pan as directed on box, using water, oil and eggs. Cool. In 2-quart saucepan, mix sugar, cornstarch and salt. Add milk and yolks. Cook and stir over medium heat until mixture boils. Boil 1 minute. Stir in butter and vanilla. Remove from heat. Cover surface of pudding with plastic wrap; cool.
2Line cookie sheet with waxed paper. Crumble cake into large bowl. Add pudding; mix well with fingers until mixture comes together. Shape into 1 1/2-inch balls; place on cookie sheet. Freeze until firm; transfer to refrigerator. Remove cake balls from refrigerator a few at a time. Dip tip of 1 lollipop stick about 1/2 inch into melted candy and insert stick no more than halfway into 1 cake ball. Dip each cake ball into melted candy to cover; tap off excess. Poke opposite end of stick into foam block. Let stand until set. Melt baking chips with shortening; drizzle over pops. Let stand until set.