Preheat the oven to 200C/180C fan/gas 6.  Remove the outer layer of cabbage leaves, shave off the root end and cut each cabbage into eighths through the root.   Lay the wedges out on a large baking tray and drizzle with the olive oil.   Roast for 25 minutes, turning them over if the tops start to really burn – they should be crisp and browned around the edges.

Meanwhile, melt the butter in a medium saucepan over a medium heat.   Once the butter has melted, stir in the flour and then turn the heat up to medium high, add the garlic and nutmeg and cook, stirring, for 3 to 4 minutes, until the mixture has dried out a little and looks sandy.   Turn the heat down to medium and slowly pour in the milk, in intervals, stirring all the time until all the milk is added and you have a smooth sauce.  Bring to a simmer, stirring constantly, then bubble for 2 to 3 minutes until the sauce coats the back of a spoon and looks glossy.   Stir in the mustard and two thirds of the cheese and season well.

Transfer the roasted cabbage wedges to a large baking dish (about 20cm x 30 cm), packing them in tightly.   Tuck in any leaves that come away from the wedges.   Pour the cheese sauce evenly over the cabbage, then mix the remaining grated cheese with the rosemary and breadcrumbs and scatter over the top.

Return to the oven for 25 to 30 minutes, until the top is golden and crisp, and the sauce is bubbling.   Allow to stand for 5 to 10 minutes before serving with a green salad or as a side to a Sunday roast.