Preheat the oven to 190oc.
Rub the inside of the ramekin soufflé dishes with unsalted butter. Add a teaspoon of sugar to each one then tilt and tap the dish rolling the sugar around until the inside is all coated.
Place the chocolate and butter in a bowl then place over a pan of simmering water and melt stirring occasionally.
Remove from the heat and allow to cool slightly before adding in the vanilla and salt.
Whisk together the egg yolks with one quarter cup of sugar. Whisk until they have lightened in colour and the mixture forms ribbons that hold for a few seconds.
Add the yolks to the cooled chocolate and fold in gently until fully combined.
Beat the eggs whites until frothy then add in the remaining quarter cup of sugar and continue whisking until they form stiff peaks.
Gently fold the eggs whites into the chocolate mixture in two halves incorporating one half fully before adding the second half.
Divide the mixture between the prepared ramekins and place in the oven.Bake for 18-20 minutes until the soufflés have risen and the tops have set.