Preheat the oven to 210C/190C Fan/Gas 7. Moisten the bread with some of the reserved fat from the confit. Use two of the slices to line two ramekin dishes, making sure the bread overlaps and is well pressed into the ramekins.
Heat a little duck fat in a saucepan over a medium heat and gently fry the shallot and garlic for 3–5 minutes, or until softened. Add the mushrooms and cook for 2 minutes.
Heat a small saucepan over a medium–high heat. Pour in the port and reduce by half. Add the stock and simmer until you have a sticky sauce.
Remove the skin from the duck and flake the meat into the pan containing the mushrooms. Add just enough sticky sauce to bind and mix. Spoon the mixture into the ramekins and seal with the remaining two slices of bread. Bake for 20 minutes.
For the sprout flowers, pour 100ml/3½fl oz water into a saucepan and heat. Add the butter and, once it has melted, add the flower sprouts. Cook for 2–3 minutes, or until wilted and hot.
Turn the Charlottes out of the ramekins onto warmed dinner plates. Serve with the remaining sticky sauce and the flower sprouts.