Method 

1st layer:
Crush the nice biscuits using a food processor, mortar and pestle or even a potato masher in a mixing bowl. Transfer to a medium bowl.
Melt the butter in 30 second bursts in the microwave until melted (around 1½ minutes). Pour the melted butter over the crushed biscuits and stir until combined.
Line a square tin (9 inch / 24cm) with baking paper or cling wrap. Pour in the crushed biscuit base and press into a flat layer using the back of a spoon.
Refrigerate for at least 1 hour.
2nd layer:
Dissolve the gelatine powder in the boiling water, stirring until   there are no lumps.
Mix the condensed milk and lemon juice in a medium mixing bowl, then pour over the gelatine mix.
Beat together using a spoon or whisk, then pour over the biscuit base.
Refrigerate until firm, around 30 minutes to one hour.
3rd layer:
In a small bowl dissolve the raspberry jelly in boiling water.
Keep stirring until all the sugar crystals in the jelly have dissolved. Pour in the cold water, give it a quick stir, and then carefully pour over the condensed milk layer. Note: If holes start to appear in the milk layer, it’s not set yet!
Pop in the fridge to set for at least 3 hours.
To serve:
Gently pull the slice out of the tray using the edges of the baking paper and transfer to a cutting board. Slice into squares or fingers and serve! Note: Clean knife between each slice for neat and even squares.