Right. So everything's in the pot, simmering. Hot pan, olive oil, sweat down your garlic and onions. Tomatoes and mushroom in, with butter. Fresh chicken stock. To make good sauce, never, ever, ever use packaged chicken stock. The only way is to buy fresh, whole chicken, and make your own broth. No shortcuts.
Just started to cook, and this will need to reduce and concentrate for at least 45 minutes. Don't be tempted to crank up the heat - your patience will be rewarded.DF