Heat oven to 200C/fan 180C/gas 6. Butter and lightly flour six 150ml ramekins.
Break up the dark chocolate and chop the butter. Melt in a bowl in the microwave for 2-3 mins on medium, stirring halfway through.
Break the eggs into a mixing bowl, add the sugar and whisk until the mixture leaves a trail on the top when the whisk blades are lifted, about 5 mins. Stir in the flour, then the melted chocolate mix.
Divide between the ramekins and push two squares of milk chocolate into the centre of each. (At this point you can leave them on the side for up to 2 hrs until you are ready to bake them.) Put on a baking sheet and bake for 12 mins exactly.
Cool for 5 mins, then turn out onto plates and sprinkle the top of each with a pinch of sea salt, if you fancy trying it. The puds are good warm or at room temperature, so there’s no panic about serving them straight away.