Melt the butter in a pan, take off the heat and add the sugars. Stir well with a whisk or fork. Allow to cool slightly for a couple mins.
Meanwhile, combine the flour, bicarb and salt in a bowl.
Add the vanilla and egg yolk to the butter/sugar mix and stir well, before stirring in the flour mix until combined.
Fold in 40g of the butterscotch chips and leave for 5 mins.
Butter your skillet, add the cookie dough and press down so it’s even.
Put in the oven at 195°C for 16-18mins.
Once ready, leave to cool for a few mins while you melt the chips for the sauce in a Bain-Marie (or heatproof bowl over simmering water).
Stir continuously until a smooth sauce.
Scoop some ice cream onto the cookie and drizzle with the sauce. Serve immediately.