Preheat the oven to 180c. Brush four small heatproof dishes with melted butter and stand them in a baking dish.
In a small saucepan melt together the butter, chocolate, golden syrup and vanilla and then remove from the heat and let cool for a few minutes. Whisk eggs into the mixture, and fold in the flour.
Divide evenly between the flour dishes and bake for 18-20 minutes, until the tops feel firm and dry.
Do not overcook because you want the inside of the puddings to be slightly soft. Serve hot with icecream or whipped cream.