Preheat the oven to 180C/350F/Gas Mark 4. Prepare your baking sheets by lining them with baking/greaseproof paper or silicone liners.
Melt the butter (in a microwave or in a small pan on the hob/stovetop) and pour it into the large bowl.
Add the sugar and beat it in vigorously with a wooden spoon.
Add vanilla extract and lightly whisked egg and beat some more.
Add the flour, baking powder and a pinch of sea salt and mix well until all combined.
Add chocolate chips, dried cranberries and chopped chestnuts and mix them all well until incorporated evenly throughout the cookie mix.
Use a heaped tablespoon (the measuring one) of cookie mixture for every cookie and scoop it onto the baking sheet leaving enough space in between the cookies to allow them to spread as they bake.
Bake for 8-10 minutes until they start to turn light brown. Once out of the oven let the cookies sit on the baking sheets for couple of minutes to firm up a bit. Transfer them onto the cooling rack to cool completely. Enjoy!