Line a 4½ by 8½ in. (12 by 22 cm) loaf pan with plastic wrap. Using two long pieces of plastic wrap, line the entire pan, pressing it down to the bottom, with enough left over to hang over the sides.
Scoop the orange sherbet into the pan, smushing down into an even layer. Freeze until firm (about 1 hour).
Now cover the sherbet layer with the vanilla frozen yogurt layer, spreading it evenly and patting it down firmly to eliminate any spaces. Place in the freezer while you prepare the crumb layer.
Place the vanilla wafer cookies in a large heavy duty zip-top bag. Press out most of the air and zip it shut. Now call in a kid. With a rolling pin or meat mallet, have your helpful child mash the cookies into fine crumbs. (OK, you can stop now.) Dump the crumbs into a bowl and add the orange zest.
In a small cup or glass bowl, combine the corn syrup and the butter. Place in the microwave and nuke on high power for 15 to 20 seconds – just until the butter is melted. Stir to combine and add to the wafer crumb mixture, tossing until it is thoroughly mixed. Spread the crumb mixture over the frozen yogurt and press it down firmly to cover everything evenly. Fold the plastic wrap over the crumbs and put the pan back in the freezer for at least 2 hours or overnight.
When ready to serve, remove the pan from the freezer and peel back the plastic wrap. Place a serving plate over the top and gently turn the pan over, pulling the dessert out of the pan with the plastic. Peel off the wrap and slice to serve.