handful of chives, finely chopped, plus extra to garnish (optional)
Boil the wine or Champagne with the shallots in a saucepan until reduced by half. Add the cream and cook until you have a rich, creamy sauce.
Heat 15 g (1/2 oz) of the butter in a frying pan. Add the pancetta and cook for 2 minutes until turning golden, then add the mushrooms and cook for 3 minutes until browned all over. Add to the sauce with the oysters and their liquor and cook for 2 minutes.
Meanwhile, slice the lid off each brioche and pull out most of the bread inside. Melt the remaining butter in a small saucepan and brush all over the inside of the brioche. Place on a baking sheet in a preheated oven, 200°C (400°F), Gas Mark 6, for 5–10 minutes until crisp.
Stir the chives into the sauce, then spoon into the brioche pots, scatter with more chives, if you like, and serve.