Red wine sauce (or other sauce for a Wellington)

[ReviewingTheSituation]

NB : has to be vegetarian

I'm making a celeriac Wellington, and I think it needs a sauce.
Most recipes for red wine sauce either use meat stock, or are really faffy.
Any recommendations for a veggie red wine gravy, or alternative sauce to go with a veggie wellington?

(I don't have any porcini mushrooms, which seem to be a popular ingredient in a veg sauce, or any stock cubes).

There's a nice tes wine sauce on bbc site from Michel Roux.