Brown the mushrooms: Heat a dry pan over high heat. Add Fable in batches — don't crowd. Let it sit and char, 3-4 mins per side. Don't stir. You want deep browning, not steaming. Season lightly with salt. Set aside.
Soffritto: In a heavy-based pot or Dutch oven, heat olive oil and butter over medium. Add onion, carrot, celery, pinch of salt. Cook low and slow for 10-12 mins until soft and starting to caramelise. Don't rush this.
Build: Add garlic, cook 1 min. Add tomato paste, stir and cook 2 mins until it darkens slightly.
Deglaze: Pour in wine, scrape up any fond. Let it bubble and reduce by half (3-4 mins).
Braise: Add browned mushrooms, crushed tomatoes, stock, soy sauce, Marmite, herbs, pepper, nutmeg. Stir well.
Slow cook: Bring to gentle simmer. Cover with lid slightly ajar, reduce heat to low. Cook 1.5-2 hrs, stirring occasionally. The sauce should reduce, darken, and become rich and glossy. Add a splash of water if it gets too thick.
Finish: Remove herb sprigs and bay leaves. Stir through cold butter for gloss. Taste — adjust salt, pepper, splash of wine or sugar if it needs brightness.
Serve: Toss with pappardelle or tagliatelle (wide ribbon pasta). Finish with fresh parsley.