Preheat your oven to 180 degrees fan force - or 200 degrees without fan. I do prefer to cook with fan for these as I believe it really does make a difference! Line two large cookie sheets with silicone baking liners if you have them and pop them aside.
In a large bowl place the melted butter. Add both sugars and beat with hand held beaters on high for 2 minutes until well incorporated.
Add in the egg and the extra egg yolk. Beat again and your mixture will become thick and glossy. Add the vanilla extra and beat a final time.
Toss in the GF flour and mix gently to combine. Be sure to get all of the melted butter mixture from the base of the bowl, otherwise you'll have oily bits in your cookies.
Add the chocolate chips to your cookie mixture and stir through. Now pop your cookie mix to the side for 10 minutes and let it rest. If you're truly invested in the perfect cookie then go ahead and wrap your cookie dough in glad wrap and pop it in the fridge overnight and bake tomorrow. But seriously... who has time for that?
While the cookie dough is resting it will harden up. You want it to be solid enough that it doesn't keep running when you scoop up a spoonful. Now scoop a rough tablespoon onto your cookie trays leaving a good 10 cm between each cookie as a minimum. These babies S.P.R.E.A.D! Pop them straight into your moderate oven and bake for 10-15 minutes.
I say 8-10 minutes as it will vary oven to oven and on just how BIG a tablespoon of dough you use. Mine take 10 minutes! So keep on eye on them after the first 10 minutes. You want a generally golden cookie with a little lightness in the middle and darker to the edges.
Remove from the oven and leave them to cool on the tray for 5 minutes before transferring to a wire rack to cool.
If you can avoid eating them all in one sitting they do keep up to 5 days in a sealed air tight container!