UK Dopers: need help with "Mushroom ketchup"

I was buying a delicious product made by a Brittish company (Burgess), that was labeled “mushroom au jus”. Sadly, I have been told that I won’t be able to get it in the U.S. anymore.

I have since found out it also goes by the name “mushroom ketchup”, although it is simply a strongly-flavored, completely liquid substance (and in no way resembles the tomato-based stuff we in the U.S. know as ketchup).

A bit of internet research has turned up a recipe or two, but they all seem to have some solids left in the finished product. I’m not sure how close any of the recipes I have found would be to what I was buying.

Anyone have any good recipes for mushroom ketchup? Any tips for cooking with it are appreciated as well!