Blend the cashews with ½ cup water into a very thick cream. Set aside.
Heat oil in a large saucepan. Add the onions and garlic along with some salt and pepper and saute for five to six minutes over medium heat. The onions should brown nicely so your sauce has great flavor, but don't let the garlic burn. Stir frequently.
Add the mushrooms to the pan along with the apple cider vinegar. Saute until the mushrooms have expressed most of their water and it has evaporated, another five to six minutes over medium-high heat. Now add the flour and stir until it gets absorbed into the mushrooms.
Stir in the rosemary, then pour the vegetable stock in, stirring constantly, so the flour dissolves in it. Bring the stock to a boil. It will look very soupy at this stage, but don't worry -- you need to let the stock reduce to about four cups, which will take about 10-15 minutes over high heat. Stir occasionally to ensure nothing sticks to the bottom.
Once the sauce has reduced and is quite thick, season with salt and pepper. Wait until the sauce has cooled a little or, if doing this while the sauce is still hot, very carefully strain it into a large bowl.
Pour the sauce back into the saucepan and bring to a boil over medium-low heat. Stir in the liquid aminos or soy sauce and cashew cream. Turn off the heat and pour over the meatballs. Garnish with parsley and serve hot or warm.