Pre-heat your oven to 180C Fan/400F/Gas Mark 6, and line a few baking trays (or however many you own) with baking paper
Mix the butter, caster sugar and light brown soft sugar together ideally in an electric stand mixer with the paddle attachment
Add the egg and vanilla extract, and mix them in until well combined
Mix in the plain flour, baking powder, salt, bicarbonate of soda and mixed spice
Then mix in the pecans and white chocolate chips
Divide the cookie dough into portions, roll them into balls using your hands. Chill them for 30 minutes in the fridge for thicker cookies, or bake them straight away for flatter cookies
When you're ready to bake, put them onto lined baking trays, leave space between the cookies as they will spread
Bake the cookies for 12-14 minutes until they are golden brown around the edges, leave them on the tray for at least 5 minutes (althought 10 minutes is ideal) before carefully removing and placing on racks to cool fully
Once the cookies are fully cool, mix the decoration ingredients together. Add the water slowly as you may not need it all. I like to put the icing into a small piping bag to control the drizzle, or you can use a fork and flick it over the cookies
Store in an airtight container and eat within 3 days. They can also be frozen for up to 3 months