Heat the oven to 180C/160C fan/gas 4. Line an 8inch square tin with greaseproof paper.
Measure the butter and sugars into a bowl and beat thoroughly until evenly blended.
Add each egg one at a time until each are incorporated. Mix in the flour then stir in the chocolate chips.
Once all the ingredients are combined, tip them into the tin and spread the cookie dough out until its an even layer across the bottom of the tin.
Bake for about 20 minutes but make sure to check it often to ensure it doesn't burn. The base should be a light golden colour.