Mary Berry Porcini, Wild Mushroom, and Watercress Gratin Recipe

I made this on a damp, chilly evening when I needed something cozy but not too heavy. I didn’t expect much—just wanted to use up some mushrooms and greens—but it turned into one of those “why isn’t this a main course?” moments.

Of course, the first time I rushed the porcini soaking and ended up with gritty bits in the sauce. Not ideal. Soak them properly and strain the liquid like your life depends on it. Once I nailed that, the flavour was deep, woodsy, and so much richer than it had any right to be.

If you want a gratin that feels fancy but uses humble ingredients, this is your dish.

THE SECRET BEHIND THIS BAKE

• The porcini soaking liquid becomes the base of the sauce. It’s earthy, savoury, and transforms a simple roux into something special.
• Fresh mushrooms + greens add texture and brightness. The mix of oyster, button, kale, and watercress is so satisfying.
• No cheese overload. Just a good layer of Parmesan on top—flavourful but not greasy.

INGREDIENTS + WHY THEY MATTER

• Dried porcini (30g) + boiling water (300ml) – Soak for at least 30 minutes. Don’t skip. Adds depth and umami.
• Oyster + button mushrooms (350g + 200g) – Two textures: soft and juicy, and slightly firm.
• Garlic (2 cloves) – Crushed for background warmth.
• Kale + watercress (115g + 150g) – Balanced greens. Kale gives body, watercress adds peppery bite.
• Butter + flour (55g each) – Classic roux base for the sauce.
• Milk (400ml) – Use whole milk for best texture.
• Double cream (2 tbsp) – Just enough to round things out.
• Parmesan (115g) – Adds saltiness and that golden finish on top.

MAKING IT YOURS (WITHOUT RUINING IT)

• Swap greens? Yes—baby spinach or Swiss chard both work if you can’t find watercress.
• Want it richer? Add more cream or top with a handful of grated Gruyère alongside the Parmesan.
• Make it vegan? Use plant-based butter, milk, and oat cream + nutritional yeast for cheesy flavour. It’s doable (I tried!).

MISTAKES I’VE MADE (AND HOW TO AVOID THEM)

What Went Wrong	Why It Happens	How to Fix It
Gritty sauce	Didn’t strain the porcini soaking liquid	Always pour through a fine sieve or muslin
Mushrooms went soggy	Overcrowded the pan	Cook in batches with high heat
Cheese didn’t melt nicely	Used pre-grated Parmesan	Grate it fresh for even melting

HOW TO MAKE MARY BERRY’S PORCINI, WILD MUSHROOM, AND WATERCRESS GRATIN

1. Soak porcini: Pour boiling water over dried porcini and soak for 30 mins. Strain and reserve the liquid. Chop the softened mushrooms.
2. Cook mushrooms: In batches, fry oyster and button mushrooms with garlic in oil + butter until golden and soft. Don’t crowd the pan. Set aside.
3. Wilt greens: Fry kale in ½ tbsp oil until wilted. Repeat with watercress. Set aside.
4. Make sauce: In another pan, melt butter, stir in flour, and cook for 30 seconds. Gradually whisk in 200ml porcini liquid and all the milk. Cook until thickened, stir in cream + half the Parmesan. Season well.
5. Assemble: Preheat oven to 200°C (180°C fan). Layer half the mushrooms and greens in a baking dish. Mix the rest with the sauce and pour over the top. Finish with remaining Parmesan.
6. Bake: 25 minutes until golden and bubbling at the edges.

TIPS FROM MY KITCHEN

• I always strain the porcini liquid twice—once through a sieve, then through a bit of muslin cloth. It makes all the difference.
• Let it rest 10 minutes after baking—it thickens and cuts more neatly.
• Great as a main with crusty bread or a roast dinner side.

STORAGE + SERVING

• Fridge: Keeps 2 days in an airtight container.
• Reheat: Oven at 180°C for 5–10 mins. Avoid the microwave if you want to keep that top crust.
• Freezer: Not ideal—cream and greens can go watery. Best fresh or chilled, not frozen.

FREQUENTLY ASKED QUESTIONS

Q: Can I prep this ahead of time?
A: Yes! Assemble it up to the baking step and store in the fridge for 24 hours. Bake when ready.

Q: What can I use instead of porcini?
A: Dried shiitake mushrooms work in a pinch, but porcini have the richest flavour.

Q: Is this a side dish or a main?
A: Either! I serve it with roast chicken or a big salad and crusty bread. It holds its own.

Q: Can I make this gluten-free?
A: Yes—just swap the flour for a 1:1 GF blend. The sauce still thickens beautifully.

Try More Recipes:

• Mary Berry Swiss Chicken, Spinach, And Mushroom Bake
• Mary Berry Somerset Mushroom Soup
• Mary Berry Garlic Mushrooms and Cured Ham on Toasted Brioche