This makes a great brunch or breakfast dish. I've served hollandaise sauce on the egg here, but making it is quite an involved process, so you might want to do without it.
Try to buy those larger field or Portobello mushrooms if you can – there are some pretty big ones on the market these days.
4 large field or Portobello mushrooms
A couple of knobs of butter, softened
4 large hen or duck egg
Hollandaise sauce, optional
For the crust
A couple of good knobs of butter
1 small onion, peeled, halved and finely chopped
6 rashers of rindless, smoked streaky bacon, finely chopped
50-60g fresh white breadcrumbs
2tbsp chopped parsley
Salt and freshly ground black pepper
Preheat the oven to 200C/gas mark 6. To make the crust: melt the butter in a pan and gently cook the onion and bacon for 2-3 minutes until soft.
Remove from the heat, stir in the breadcrumbs and parsley and season.
Place the field mushrooms on a grill tray, rub over the butter and season, then cook for about 3-4 minutes on each side.
Turn the mushrooms dark side (gills) up and spoon over the crust making a small indentation in the centre for the egg. Bake for about 10-12 minutes or until the crust is golden.
Meanwhile, poach the eggs and drain on kitchen paper, then place one in the centre of each mushroom, spoon over the hollandaise, if using, and serve.