Prepare a large sponge roll tin (approximately 34cm x 23cm) either by lining with a compostable baking paper or reusable liner.
Melt together in a large pot, the butter, condensed milk, and cocoa.
Blitz the biscuits until a fine crumb.
Take the pot off the heat once all the ingredients have melted and add the biscuits, vanilla, raisins and raspberry lollies.
Press the mixture into your lined tin and use the back of a spoon to smooth the mixture into the corners and get an even surface.
While the base is still soft, sprinkle on the marshmallows and nuts and press down into the base. Place in to the fridge to set (use a paper towel in the surface if there is an excess of butter).
Melt the chocolate in a bowl over a boiling pot of water (known as the double boiler method). Pour the chocolate over the slice making sure to sway back and forth across the entire slice as you pour the chocolate. Use a spatula to evenly spread the chocolate without disrupting the marshmallows and nuts too much. Place in the fridge once again to set.
Once the slice is set use a knife dunked in hot water to slice into even pieces. Store in an airtight container in a cool spot to avoid the chocolate going soft.
