This is Nigella's evily good recipe for her Totally chocolate chocolate chip cookies. I have never made anything with three types of chocolate before. Seems so indulgent but just what the mental health doctor ordered on a rainy day with a hot cuppa and a lie down.
I always use less sugar than Nigella in all her recipes.

125 grams dark chocolate (minimum 70% cocoa solids)
150 grams plain flour 
30 grams cocoa powder (sieved)
1 teaspoon bicarbonate of soda 
½ teaspoon salt
125 grams soft butter 
75 grams soft light brown sugar
50 grams white sugar
1 teaspoon vanilla extract
1 large egg (cold from the fridge)
350 grams dark chocolate chips (or semi sweet chocolate morsels) I only used about 100g and it was enough for me.

1. Preheat the oven to 170°C/gas mark 3/325ºF. Melt the 125g / 4oz dark chocolate either in the microwave or in a heatproof dish over a pan of simmering water.
2. Put the flour, cocoa, bicarbonate of soda and salt into a bowl.
3. Cream the butter and sugars in another bowl. Add the melted chocolate and mix together.
4. Beat in the vanilla extract and cold egg, and then mix in the dry ingredients. Finally stir in the chocolate morsels or chips.
5. Scoop out 12 equal-sized mounds - an ice cream scoop and a palette knife are the best tools for the job - and place on a lined baking sheet about 6cm apart. Do not flatten them. (NIgella makes HUGE cookies - I made about 30 medium-sized ones)
   
6. Cook for 18 minutes, testing with a cake tester to make sure it comes out semi-clean and not wet with cake batter. If you pierce a chocolate chip, try again.
7. Leave to cool slightly on the baking sheet for 4-5 minutes, then transfer them to a cooling rack to harden as they cool.