For the sauce, fry the sliced button mushrooms in the butter until all the water is evaporated and the mushrooms are nicely coloured. Add the Madeira wine, flame off the alcohol and reduce to a syrup texture. Add the veal fond and reduce by two thirds. Add the Debic Culinaire Original. Reduce by one third of the volume. Pass through a sieve, season the sauce with salt and balance the acidity with some reduced wine.
For the ketchup, blitz the mushrooms in a food processor. Mix with the salt and leave to macerate overnight. Weigh out the vinegar, herbs, spices and shallots. Squeeze out all the juice from the mushrooms and bring to the boil. Add the vinegar mix and reduce to 250 ml. Thicken the ketchup with the cornflour and keep refrigerated.
Slice the mushrooms in 5 mm thick slices and warm through in the mushroom ketchup.