Place the dried ceps in a bowl and cover with 250 ml boiling water. Soak for 15–20 minutes, then lift out, squeeze gently, finely chop, and strain the soaking liquid through a fine sieve to remove grit. Chop the onion and rosemary, and mince the garlic.
Heat the olive oil or vegan butter in a medium saucepan over medium heat. Add the onion and cook for 8–10 minutes until softened and lightly golden, stirring occasionally.
Add the garlic, rosemary, and thyme. Cook for 30 seconds until fragrant.
Sprinkle in the flour and stir for 1 minute to form a paste.
Pour in the red wine slowly, scraping the bottom of the pan to lift any browned bits. Simmer for 2–3 minutes until slightly reduced.
Add the chopped ceps, strained soaking liquid, vegetable stock, soy sauce or tamari, and Dijon mustard. Bring to a gentle simmer and cook for 10–12 minutes, stirring occasionally, until the gravy thickens.
Stir in the redcurrant jelly until fully dissolved. Season with salt and black pepper, adjusting the consistency with a splash of stock or water if needed.