Preheat the oven to 200°C Peel and roughly chop mushrooms, including the stems.
In a non-stick heavy-based pan, add some liquid and cook the onion until they're soft. Add the garlic and cook for 1 minute after. Add the mushrooms and cook until soft. Sprinkle the flour over the top and stir for a minute.
Stir in the stock, add thyme and bring to the boil. Reduce the heat to simmer, covered, for 10 minutes. Allow to cool before lightly processing the mix with a stick. I like mine with a lot of texture so do it to your own taste.
Stir in the sherry and the evaporated milk.
Pour mix into 4 ovenproof bowls or individual serving casserole dishes/ramekins. Use small deep dishes in any case so the pastry doesn’t flop into the soup.
Cut rounds of pastry slightly larger then the bowl tops (or do this first tracing bowl tops)and cover each bowl with the pastry.
Seal the edges and give each pastry top a light brush with the egg or the no fat milk.