In a large bowl, mix the mushrooms and the salt together and cover with clingfilm for 24 hours. Every so often, press down the mushrooms and stir with a wooden spoon until they start to release ...

The 1812 recipe from James Mease is the first appearance ... "So rather than soybeans, let's do mushrooms." So they had mushroom ketchup. "Let's do fish." And so they had fish ketchup.

These BBQ pulled mushroom sandwiches are essential at your next vegan barbecue. Enjoy them with creamy vegan coleslaw.

Ketchup will last longer when stored in the fridge, but its high sugar and vinegar content means it isn't necessary for short periods of time.

Bring to the boil, stirring constantly, then add the mushroom ketchup and stock a little at a time until it has all been added and you have a fairly thin gravy. Taste and add more seasoning if needed.