Many thanks goes to J from Wales at the Down to Earth Forum for finding the recipe for me....
Here is what took place.
Mushroom ketchup (from Preserving, by Oded Schwartz)
2 kg / 4 lb large flat-cap mushrooms
60 g / 2 oz dried ceps (optional) (I never used these)
150 g / 5 oz salt
300 g / 10 oz shallots, unpeeled, quartered
5 cm / 2 in piece of ginger root, bruised
125 ml / 4 fl oz port
1 Tbsp cloves
2 tsp crumbled mace blades ( I used roughly chopped nutmeg pieces)
Put the fresh mushrooms in the food processor and coarsely chop. Arrange in thin layers with the dried ceps (if using) in a casserole dish, sprinkling each layer with some of the salt. Cover and leave to stand for 24 hours.
Pour into hot sterilised bottles and seal. I am to tired tonight to bring back to the boil, but I will do it first thing in the morning. For now, I will just refridgerate it overnight. I have some small brown glassed bottles, I think I will bottle this in. That way I only have a small amount open at any one time.
Water bath for 20 minutes, then check the seals. The ketchup will be ready in one month, but improves with keeping.