Place the digestive biscuits in a clean ziploc or plastic bag and run a rolling pin over it a few times till all the biscuits are crumbs.
Put the butter in an microwave-safe bowl and microwave it for 30 seconds or till completely melted. Make sure you don't let it burn. This can also be done on the stove.
To the melted butter, add the crumbled digestive biscuits, peanut butter, sugar & vanilla extract. This when you can dig in your hands while your kid adds in one item after the other, provided they have been set out in the right measure beforehand. Mix all ingredients thoroughly.
Line the baking tin or tray with the aluminum foil. With a brush, grease the foil with some butter. This will help the squares come off the tray easily.
Dump the peanut butter mixture on the prepared tray and flatten it out with a spatula or the back of the spoon. A smaller tray will give you thicker squares, and a larger one will give you thinner bars. Place the tray in the refrigerator to firm up.
Break the chocolate into small pieces and place in a microwave -safe bowl along with the milk & half tablespoon of butter. Microwave for 40 seconds or till completely molten. You can also melt the chocolates in a double boiler on the stove top.
[For a double boiler, place a high rim pan or narrow mouthed handi and keep the heat safe bowl of chocolates on top of it. Make sure the bottom of the bowl gets the steam from below but doesn’t touch the hot water. Touching the water below will make the chocolate grainy. Stir well.]
Pour the chocolate above the set biscuit-peanut butter mixture. Tap the tray to uniformly distribute the chocolate topping over the base. Chill again for at least 4-6 hours. If you like, you can use another layer of chocolate sauce over the chilled chocolate topping to have two layers of chocolate.
Garnish with drinking chocolate powder or sweetened cocoa on top. You can also sprinkle chocolate vermicelli or chocolate shavings. When everything is firm and completely set, dip your knife into lukewarm water, cut into squares and serve.