Preheat the oven to 170'C.
Melt the butter and the chocolate in a bowl over a pan of simmering water.
Whisk the eggs and the sugar together. Once doubled in volume, gently fold in the chocolate, the flour and the pecan nuts.
Butter silicone muffin moulds and dust with flour. Pour the mixture into the moulds so that they are 3/4 full. Transfer to the oven and cook for 10-12 minutes.
Remove from the moulds and allow to cool for a few minutes.
Break the chocolate into small pieces and place in a bowl.
Place the cream, condensed milk, butter, vanilla extract and the cinnamon stick in a saucepan and bring to a gentle simmer. Remove the cinnamon stick and then pour the mixture over the chocolate. Stir until you have a smooth and glossy sauce.
Spoon the sauce over the brownies to serve.
«Remove the sauce from the heat as soon as it starts to simmer - it just needs to be hot enough to melt the chocolate.»