Apologies for taking so long to find this. It’s been years since I made mushroom roast: it works best (in my opinion) as the main dish in a festive dinner. It’s a considerable amount of work to make, unless you have a food processor, and even if you do – don’t try to process the mushrooms in it. Slice them properly. I’m not just being pickily low-tech: you can make the breadcrumbs any way that suits you (my parents used to use child labour), you can slice the onions perfectly well in a food processor: but mushrooms turn to mush too easily if they’re fed through a processor.
The basic ingredients are: mushrooms, breadcrumb, onions, and cheese. You may also want: garlic, herbs, vegetable stock, and an egg or two.
The basic process is: cook onions in butter to a savoury, soft mess (with herbs and garlic). Add mushrooms, and cook over a low heat until the mushrooms are cooked enough to suit you. You want a fairly soft and semi-liquid paste of onions and mushrooms. Stir in the breadcrumb. If it’s too dry, add some vegetable stock – you want a fairly moist mixture. Stir in grated cheese. When you are ready to bake the roast, add an egg or two (depending on the size of the roast) and put the whole mixture in a deep, greased casserole dish and bake until it’s crusty on top.
Proportions are important.
For every kilo of mushrooms, you want a kilo of breadcrumb, 500-750 grammes of onions, and 500-750 grammes of hard cheese. This size of roast will take about 90 minutes to bake in a medium hot oven. [Update: Yes, this is a LOT of mushrooms: it makes a big savoury for a festive meal. You can always halve or even quarter the amount for a smaller dish... just keep the proportions, by weight, the same.]
I like garlic… lots of garlic… and do the obvious: subtract the weight of the garlic from the weight of the onions. See the nut roast recipe for thoughts about herbs. (There is also the foodpairing website, though I find it more fun than useful.) Instead of regular vegetable stock, you can use Marmite, a couple of teaspoonfuls in about 150ml of boiling water – do not add the whole quantity, just mix it up and stir it in until the texture looks right: you’re after a glopping consistency, soft and moist, not liquid).
This is not a vegan recipe. The cheese in the mushroom roast isn’t just there to make it coherent: the combination of cheese and mushroom is what makes this a rich, glorious dish. Figure on about one egg to every half-kilo of breadcrumb – but add the eggs one at a time, to make sure the texture stays right. You don’t want to over-egg the pudding.