Why You’ll Love This Portobello Mushroom Caps with Walnut Pesto

• It’s a flavour powerhouse. The combination of the umami-rich, roasted portobello mushrooms and the nutty, garlicky, herby walnut pesto is just next-level delicious. Each component complements the other so perfectly.
• It’s surprisingly easy and fuss-free. You don’t need any fancy techniques here. A quick blend for the pesto, a simple roast for the mushrooms, and you’re pretty much done. It’s the kind of recipe that looks impressive but is secretly low-effort.
• It’s incredibly versatile. Serve these as a main course, slice them up for a salad topper, or even use them as a gourmet burger patty alternative. They work wonderfully hot, warm, or even at room temperature.
• It feels indulgent but is packed with good stuff. You get that satisfying, meaty texture from the mushrooms and healthy fats from the walnuts and olive oil. It’s a meal that leaves you feeling nourished and completely satisfied, without any heaviness.

Ingredients & Tools

• 4 large portobello mushrooms
• 3 tbsp olive oil, divided
• 1/2 tsp sea salt, plus more to taste
• 1/4 tsp black pepper
• 100 g walnuts
• 50 g fresh basil leaves, packed
• 1 large garlic clove
• 60 g grated Parmesan cheese (or a vegetarian alternative)
• Juice of 1/2 a lemon
• 60-80 ml extra virgin olive oil

Tools: A baking sheet, food processor or high-speed blender, a small bowl for mixing.

A quick note on the ingredients—using fresh, good-quality basil is key for a vibrant green pesto, and toasting the walnuts, which we’ll get to, makes a world of difference. Don’t be shy with the garlic, either; roasting the mushrooms tames its sharpness beautifully.

Serves: 2 (as a main) or 4 (as a side) | Prep Time: 15 minutes | Cook Time: 20 minutes | Total Time: 35 minutes

Before You Start: Tips & Ingredient Notes

• Choosing your mushrooms. Look for portobellos that are firm, with a dry surface and tightly closed gills (the dark brown part underneath). They should feel heavy for their size and have a pleasant, earthy smell.
• To wash or not to wash? There’s a big debate here! I give mine a very quick rinse and then pat them thoroughly dry with a kitchen towel. The key is to not let them sit in water, as they’ll absorb it like a sponge and steam instead of roast.
• The walnut factor. Toasting the walnuts before blending is non-negotiable for the best flavour. It wakes up their oils and gives the pesto a deep, nutty aroma that raw walnuts just can’t provide. It takes just a few minutes but elevates the entire dish.
• Pesto consistency. Everyone likes their pesto a little different. Start with the lower amount of olive oil, then blend and check. You can always add more to get it to your preferred consistency—some like it thick and spreadable, others prefer it a bit saucier.

How to Make Portobello Mushroom Caps with Walnut Pesto

Serving Suggestions

Complementary Dishes

• A simple arugula salad — The peppery bite of arugula dressed with just lemon juice and olive oil provides a fresh, crisp contrast to the rich, earthy mushrooms.
• Creamy polenta or mashed potatoes — Spoon the mushroom caps over a soft, creamy base to catch all the delicious juices and pesto that will inevitably escape.
• Grilled asparagus or zucchini — Some charred, seasonal vegetables on the side make for a complete and beautifully colourful plate.

Drinks

• A light-bodied Pinot Noir — The earthy notes in the wine mirror the mushrooms beautifully, while its acidity cuts through the richness of the pesto.
• A crisp, citrusy pale ale — The hoppy bitterness is a fantastic palate cleanser against the umami and garlic flavours.
• Sparkling water with lemon — For a non-alcoholic option, the bubbles and citrus keep everything feeling fresh and light.

Something Sweet

• Dark chocolate and orange pots de crème — The intense, bitter chocolate and bright orange are a sophisticated and not-too-heavy way to end the meal.
• Lemon sorbet with fresh berries — This is the ultimate palate-cleanser; zingy, refreshing, and the perfect little bite after a savoury main.
• Almond biscotti — A nutty, crunchy cookie to nibble on with a cup of espresso ties back to the walnut theme in a lovely way.

Top Mistakes to Avoid

• Mistake: Not drying the mushrooms properly. If the mushrooms are wet, they’ll steam and become soggy instead of developing that lovely, roasted, caramelised edge we’re after. Pat them dry!
• Mistake: Skipping the walnut toasting step. I know it’s an extra step, but raw walnuts can have a slightly bitter edge and lack the deep, toasty flavour that makes this pesto special. It’s a game-changer.
• Mistake: Over-processing the pesto. You want a pesto with a bit of texture, not a completely smooth paste. Pulse the ingredients until they are just combined. A little rustic texture is a good thing here.
• Mistake: Overcrowding the baking sheet. Give the mushrooms some space! If they’re too close together, they’ll steam each other. You want the hot air to circulate freely for even cooking.

Expert Tips

• Tip: Make extra pesto. This walnut pesto is too good to make in just a small batch. Double it and store the extra in a jar in the fridge with a thin layer of olive oil on top. It’s amazing on pasta, sandwiches, or swirled into soups.
• Tip: Get creative with the cheese. While Parmesan is classic, try swapping in a sharp Pecorino Romano for a saltier kick, or even a creamy goat cheese for a different tang.
• Tip: Add a breadcrumb crunch. For a bit of textural contrast, mix some toasted panko breadcrumbs with a little olive oil and parsley, and sprinkle it over the pesto-filled mushrooms before serving.
• Tip: Prep ahead for easy entertaining. You can clean the mushrooms and make the pesto a day in advance. Store them separately in the fridge, then just roast the mushrooms and assemble when your guests arrive.

FAQs

Can I make this recipe vegan?
Absolutely! It’s very easy to veganize. Simply omit the Parmesan cheese from the pesto. You might want to add a pinch more salt to compensate, or even a tablespoon of nutritional yeast, which gives a lovely, cheesy, umami flavour that works perfectly here. The rest of the recipe is naturally vegan.

How should I store leftovers?
Store any leftover mushroom caps and pesto separately in airtight containers in the refrigerator. The mushrooms will keep for up to 2 days, and the pesto (with its layer of oil on top) for about 5 days. The mushrooms will release more liquid upon reheating, so I actually love them cold, sliced over a salad the next day.

Can I use a different type of nut?
Of course! While walnuts are our star, pine nuts would bring you back to a more classic pesto. Almonds or pecans would also work wonderfully, just be sure to toast them first to bring out their flavour. Cashews would make a creamier, milder pesto. It’s a great way to use what you have on hand.

My pesto turned out bitter. What happened?
Bitterness can come from a couple of places. First, if you over-blended the basil, it can sometimes oxidize and turn bitter. Secondly, walnuts can have slightly bitter skins. If yours are particularly strong, you can toast them and then rub them in a clean kitchen towel to remove some of the skins before blending.

Can I grill the mushrooms instead of roasting them?
Yes, grilling adds a fantastic smoky flavour! Brush the caps with oil and grill over medium-high heat for about 4-5 minutes per side, until tender and nicely marked. Just be careful, as they can cook a bit faster on the grill than in the oven.