Preheat the oven to 190 degrees C.
Brush 2 ramekins with melted butter and coat with caster sugar. Tap out excess and set aside in the refrigerator.
Melt the chocolate and set aside.
Melt the butter in a saucepan. Add in the flour, whisk and cook for a minute.
Reduce the heat to low and whisk in the milk and cook until the mixture thickens (about 2-3 minutes). Add this to the melted chocolate and mix to combine. Add in the salt and mix well.
Once the mixture has cooled slightly, add in the yolks and mix till well combined.
Whisk egg whites with cream of tartar in a separate bowl. Add in sugar gradually and whisk to stiff peaks.
Gently fold the egg whites in three additions into the chocolate mixture.
Divide the batter between the prepared ramekins and level out. Clean the sides of the ramekin and bake in the preheated oven for 12-15 minutes until the souffles are well risen.
Remove from the oven and dust with some confectioner’s sugar. Serve immediately.