• Place 12 teaspoons of Nutella onto a baking tray lined with parchment paper, and freeze until solid - about 1 hour.

For the Pastry

• Sift the flour into a large bowl. Add the butter and, using your fingertips, rub into the flour until the mixture resembles fine breadcrumbs. Stir in the sugar.
• In a small jug, or mug, lightly beat the egg yolk with the vanilla extract and water. Add to the flour mixture, and mix in using a knife. Gather together to make a soft dough.
• Wrap the dough in clingfilm, and chill for at least 30 minutes before use.
• Preheat the oven to 180C/350F/Gas 4, and grease a 12-hole muffin pan. On a lightly floured surface, roll out the pastry, and using a pastry or cookie cutter, cut out 12 circles/fluted circles, and press into the prepared pan. You may need to re-roll the pastry to get 12 circles.

For the Cookies

• Whisk together the flour, baking powder, cornflour, baking soda, and salt. Set aside.
• Whisk together the butter and sugars until combined. Add the egg, and vanilla, and mix until combined. Add the dry ingredients, and mix until just combined. Fold in the chocolate chips.
• Place a teaspoon of the Nutella onto the centre of each pie crust, then press 1 oz balls of cookie dough on top. Sprinkle with extra chocolate chips if desired, and bake for 15 - 20 minutes. Allow to cool in the pan for 5 minutes before cooling completely on a wire rack.
• You may have some cookie dough left over. If so, just roll into 2 oz balls, and bake for 10 - 12 minutes - enjoy!