I made a biscuit base in a tin like this. This one is a 20cm square tin. Make sure the tin is non-stick. You can also make this with short crust pastry too, but I prefer using a biscuit base. I use Hummingbirds sugar biscuit recipe but I don't add the cream of tartar.
Now, weigh out 150g skimmed milk powder
Then add 85g icing sugar to the skimmed milk powder.
Then add 85g Marg to the skimmed milk powder and the icing sugar
Then add about 2-3 tbsp coca powder to the skimmed milk powder mix
Now, boil the kettle. Once the kettle is boiled, get your electric mixer ready
Add a little splash of water to the mixture. Less is more. Start off with a tiny bit and then add until you have a thick, pouring consistency.
Pour the toothpaste over the biscuit base and then put it in the fridge to set.
Cut into squares and top each square with a swirl of dream topping or butter icing.