In a small saucepan, melt the butter. Continue to heat it on medium-low on the stove until it foams up and smells nutty then stir in the vanilla extract. Leave to cool for 10 minutes.

Meanwhile, either in a stand mixer or a large bowl combine the next 6 ingredients (flour through to salt). Pour in the butter and mix until it looks like moist clumpy sand with no floury patches. Add the egg and mix in for a few seconds, then the chopped chocolate and mix until well distributed - but not for too long!

Using a 1/4 cup cookie scoop**, scoop up some of the dough and smoosh it into the scoop until it's just full. Turn out onto a lined cookie tray, spacing each mound 3" apart (I managed 4 per tray). Repeat with all of the cookie dough. Cover with cling film and refrigerate for anywhere between 1 - 72 hours (the longer you wait, the better the texture and flavour!!!).

When ready to bake preheat your oven to 400 degrees F (200 degrees C). When ready, sprinkle the cold cookie dough with fleur de sel and shove into the oven immediately!! Bake for 8-11 minutes, until browned, with set edges, and a puffy, soft center. Let cool on the baking tray for a minute before transferring to a wire rack.

*You can sub the fancy salt for a scant 1/2 tsp of table salt in the dough, however you can't use table salt for sprinkling so either use the fancy salt for sprinkling or just don't sprinkle at all.

** You can just use a 1/4 cup measure (which equals 4 tbsp), then roll the dough into a ball with your hands and slightly flatten into a hemi-sphere on the baking tray.