Pre-heat your oven to 230 degrees Celsius. (450 degrees F)
Grease your ramekins or your muffin tray moulds with the EXTRA butter. Cut some grease-proof paper into squares big enough to fit in your moulds.
Scrunch the paper squares, then open them up again, from there they should fit snugly into your moulds. Once the paper squares are in the moulds, give them a quick spray with the cooking spray to ensure that those lava cakes don't stick.
Put the chocolate chips and butter in a large bowl, then heat in the microwave for about 15-20 seconds at a time stirring on each occasion. Do this until the chocolate melts (don't just blast it in the microwave, because if chocolate gets too hot, it won't melt).
Use an electric beater to beat the eggs, egg yolks and caster sugar together in a large bowl. Beat for a good 6-7 minutes until the mixture goes light, foamy and triples in size.
From there, add your chocolate and butter mixture in 3-4 intervals, stirring through on each occasion.
One the batter has been mixed well, add the cocoa powder and your vanilla, then stir through one last time.
Ladle your batter into the moulds and fill about 3 quarters of the way up. If you have made any mess around the edges of the moulds, quickly clean it up with kitchen paper. If you are using ramekins, put them on a baking tray first. Otherwise get your cakes in the oven and cook for 8-9 minutes.
Once they are done. Carefully flip them out of the ramekins onto a plate, then peel the paper away. If you cooked your cakes in the muffin molds, you can grab the paper to gently lift the cakes up, place upside down on the plate, then again, peel the paper away.
You can put a scoop of ice-cream on top if you wish, then serve straight away while hot.