1. Prepare the onions and shallots. Clean mushrooms, and then dry them as thoroughly as possible (I squeezed them in a clean kitchen towel). Mince mushrooms and set aside separately. Note: any kind of mushrooms will do nicely-- I used a mix of button mushrooms and crimini (baby bella).
2. Grab your saucepan and put in oil (as a lacto-veg, I used organic butter, but there is absolutely no reason not to use a flavorful oil in its place). Cook onions and shallots over medium-low heat until soft, sweet, translucent, and barely turning golden. DO NOT ALLOW TO BROWN at all, since it will ruin the flavor of the sauce (even if you find browned onions delicious elsewhere). This will take roughly 10 minutes.
3. Add mushroom mince and stir throughout. Continue to cook the mixture down over a medium heat, stirring every minute or so. Liquid will rise to the top while this mixture cooks; you want to cook and stir this until it ceases rising to the top. It will thicken into a lovely paste and the flavor will deepen.
4. Stir in salt, pepper, and parsley, and allow to cool. You may add walnuts at this point if desired, or even blitz them in the food processor with the dry mushrooms earlier in the recipe.
5. Enjoy small amounts of this extremely rich, slightly chunky paste as a flavoring agent in soups, stews, sauces, etc. It is DELICIOUS smeared thinly on wholegrain toast. Store leftovers airtight in refrigerator or freezer.
P.S. I used it as the spread for an open-faced sandwich featuring quickly stir-fried summer squash and red peppers and a handful of tiny tomatoes-- delicious!