Usually put a scoop of Marmite in, (other brands are available, and just as good IMHO, look for 'yeast extract'.) I use the water I have cooked the vegetables in, including the potatoes water.
I start off with frying onions, garlic very finely chopped mushròm and a few other very finely chopped root veg'. I then add a good glug of red wine. I put it on a slow simmer add herbs from the gardens, Parley, thyme, sage, basil, Chives, whatever I have. I add the Veg' water,; taste & season as I go and when happy add corn flower to thicken it. Follow instructions on the packet. Job done! Takes me a considerable time, but I love i, and th usual compliments!
Alternatively use one of the gravey mixes, Aldi and Llidl do ones that may even say for meat on them, but are Vegan. For daily use I use them. I use veg water and a drop a bit of yeast extract in. If you have any wine left over make it special by dropping some in it. So you definitely don't need to show off like me. I am use my family will agree, they just like to humour me!