Make cookies. You will need two cookies per treat. Prepare dough and roll out 3/16 in. thick. Cut using largest Cut-Out from set.
Invert whoopie pie pan and spray with vegetable pan spray. Drape dough over every other pan cavity, pressing to smooth surface. Bake 10-14 minutes, or until firm and golden brown. Cool pan on cooling grid 10 minutes. Carefully loosen bottom edges of pan using spatula. .
Fill treats. Fill one cookie with jelly candies.
Make piñata treats. Prepare royal icing. Use tip 8 and icing to pipe a line around rim of candy-filled cookie; attach second cookie. Use tip 8 and white icing to pipe an additional line around edge.
Decorate swirl. Use piping gel and a cut parchment bag to pipe swirl. Sprinkle with blue sugar