I managed to make this yesterday, totally foolproof, no baking, and with newborn and toddler in tow (since you have gaps to sort kids out while things cool etc!). It was in a Thats Life my MIL had, I've adapted it to NZ jelly sachets which have a different amount. In brackets what I used myself.
Jelly Slice
250g packet shortbread biscuits (Arnotts Arno Shortbread)
100g melted butter
3 x Weightwatchers jelly sachets (Strawberry flavour)
2 x 125g fruit yoghurt pottles (Meadowfresh Strawberries & Cream)
Lightly grease a slice tin. Crush biscuits and add melted butter. Press into tin. Mix up the 3 sachets of jelly with 3 cups of water. Set aside 1 cup of jelly mixture. Let both bowls of jelly mixture cool. Add the 2 pottles of yoghurt to the bigger portion of jelly mixture and spread over the biscuit base. Chill until set.
Gently pour/spoon remaining jelly mixture over the slice and once again chill until set.
Done!