If the Nutella and peanut butter are not soft and creamy, melt them together for a few seconds in the microwave.
In a large bowl whisk Nutella, peanut butter and butter, mixing until combined and smooth. Add crushed cookies and mix. Add 2-3 tablespoons of milk, until the ingredients start to stick together and form a dough-like consistency,and the mixture is no longer crumbly and can easily be rolled into balls.
Refrigerate the mixture for at least 30 minutes for easy rolling.
Shape mixture into balls the size of heaping tablespoons. Roll in toppings of your choice (coconut, cocoa powder, sprinkles, crushed peanuts or hazelnuts). Refrigerate for one hour.
Truffles will keep for 5 days in the fridge. They can also be frozen for up to 2 months.