In a large mixing bowl add the butter and both sugars and whisk until light and creamy. An electric whisk is easiest.
150 g unsalted butter, 80 g granulated sugar, 80 g light muscovado sugar
Add the egg and vanilla extract and whisk again.
1 large egg, 2 tsp vanilla extract
Turn on the oven and preheat to 190C/375F/Gas Mark 5
Using a fine sieve, sift the flour and bicarbonate of soda into the mixing bowl along with the salt and using a spatula or wooden spoon mix gently.
225 g all purpose flour, ½ tsp bicarbonate of soda, 1/4 tsp salt
Add the chocolate chips and stir well to combine.
200 g chocolate chips
Cover 2 baking trays with greaseproof paper/parchment.
Using a teaspoon, scoop out heaped portions of the mixture. This batch should make roughly 26 – 30 cookies.
When they are ready to be baked, pop into the oven for about 8 minutes or until they have turned a lovely golden brown. The centre however should still be mildly soft and bouncy if depressed.
Leave to cool and firm up slightly before transferring them to a cooling wire rack.
Notes
If you don't have chocolate chip, you can break up a normal chocolate bar into small chunks instead.