Method

1. Line a 32cm x 25cm baking tray with baking paper and preheat oven to 180 Celsius.
2. Cream the butter, sour cream and both sugars until pale.
3. Add eggs one at a time and mix until they are well incorporated.
4. Add the vanilla essence.
5. Add the dry ingredients (the bicarbonate soda, baking powder, sea salt and flour) and fold gently until they are well incorporated. Mix in the chocolate.
6. Smooth the mixture out onto the baking tray and if you are baking it today, let it rest in the fridge for at least at hour, otherwise you can cover the whole thing in cling film, put it in the freezer and bake it from frozen.
7. Bake the sheet of cookie in the oven for around 15 minutes, or until slightly golden. It's better for the cookie to be undercooked because it will firm up after you take it out of the oven. If you are wanting to cut it into shapes do this as soon as the cooked dough comes out of the oven.
8. Eat the offcuts!

Sour cream is great in baking. These cookies will be perfect on Christmas Eve with a glass of milk for Santa. You could make the dough in advance and freeze it.