Lightly butter a twelve hole muffin tin. Press a strip of parchment paper into each well so that both ends of the strip overhang the edges. Set the tin aside whilst making the cookie dough.

In a large mixing bowl, cream together butter and sugars until smooth and paler. Add in vanilla and mix through.

Sift in the flour, cornflour, cocoa, baking powder, bicarbonate of soda (baking soda) and salt. Mix until the mixture is evenly combined and is damp but not clumping. Tip in the egg and mix until everything is clumping together.

Divide the cookie dough evenly into twelve portions, then roll each portion into rough balls and pop one into each muffin well. Press it down into an even layer, then use a pastry tamper or the end of a rolling pin to make a dent in the middle of each, turning it into a cup or bowl shape. Pop the tin in the fridge for the dough to chill for at least an hour.

When ready to bake, preheat the oven to 180C/350F for 10 minutes. Once the oven is hot, bake the chilled cookie cups for 11 minutes until the edges are slightly firm, but the middles are still soft and squidgy. As soon as you remove them from the oven, use the pastry tamper or rolling pin to press down the middles of the cups, creating individual bowl shaped cookies. Leave the cups in the tin to firm up for 10 minutes before transferring to a wire rack to cool completely.

Once the cookie cups have cooled completely, it's time for the fun bit! Gently heat the pistachio cream until it is looser and more spoonable. It doesn't matter if its a little lumpy, it all adds to the effect!. Spoon enough pistachio cream into each cookie cup to look like a green potion, swirling the top if you can.