Pre-heat your oven to 200C/180C Fan/400F/Gas Mark 6 and grease and line the bottom of four ramekins or dariole moulds
Melt the butter and dark chocolate in a glass bowl above simmering water, then set aside. You can also melt it in the microwave, start with a 30 second blast, stir, then continue with 10 second blasts stirring in between each one
Whisk the eggs and caster sugar together
Pour the chocolate mixture into the egg mixture and whisk as you pour so the eggs don't cook
Sieve the plain flour into the mixture and whisk in
Divide the mixture between the ramekins/moulds, leave about ½cm room for them to rise and bake for 12-13 minutes. The baking time does depend on your oven, so if you're making these for a dinner party try and test them a few days before
Let them cool for a couple of minutes, then use a butter knife to loosen around the edges, put a plate or bowl on top of the ramekin and flip the whole thing over and then remove the ramekin and peel the baking paper off the top
Serve immediately with a dusting of icing sugar or cocoa powder, and some good quality vanilla ice cream