Twice Baked Walnut & Chocolate Chip Cookies

BBC2 seems determined for me to put back some of the two stones of weight I lost recently and here is his latest ploy:

I know it can be a bit of extra work but they are worth it, if you like a sweet crispy biscuit.

Ingredients:
60g/2 oz chopped walnuts
40g/ 1 ½ oz milk chocolate chips
125g/ 4 oz unsalted butter
100g/ 3 ½ oz caster sugar
50g/ 45g/ 1 ½ oz dark brown sugar
1 egg
175g/ 6oz plain flour
½ teaspoon baking powder
½ teaspoon vanilla extract

Method:
Preheat oven to 180 Fan
In a large pan melt the butter, remove the pan from the heat and with a wooden spoon mix both sugars until well mixed the in the butter, it may not be totally incorporated, but don’t worry. Now, in a separate bowl, whisk the egg and the vanilla extract together then add to the cool sugar mixture stirring until combined. Now sift the flour and baking powder into the pan and mix well, you can now mix in the chopped walnuts and chocolate chips until fully combined.
You will need to two baking sheets greased. Put a tablespoon of the mixture onto the baking sheet, making sure you leave room for them to spread. The mixture should give you 16 cookies depending on the size you make them.
Place in the oven and cook for 12 to 15 minutes until golden brown and just firm, take them out of the oven and let them stand for 5 minutes. Whilst this happens, turn down the oven temperature to 150 Fan.
When the 5 minutes is up transfer the cookies to a wire rack, they will not spread anymore so try to get them onto one rack and place the wire rack onto a baking sheet then back in the oven for 10 minutes or so.
The wire rack is to ensure good heat circulation, as the cookies have a cake like texture at this point, all you are doing is ensuring they cook through and crisp up. When cool store in an airtight container.
You can change the nuts for dried fruit should you have an allergy, play with different combinations as to what suits your taste.