Portobello Stuffed Mushrooms

Ingredients

• 4 largePortobello mushrooms
• 30 ml (2 tablespoons)olive oil
• ½ smallonion, finely diced
• 2 clovesgarlic, minced
• 2 sprigsfresh thyme, stalks removed
• 60 g (2 cups)fresh spinach, chopped
• 55 g (½ cup)breadcrumbs
• 55 g (½ cup)Gruyère cheese, shredded
• 25 g (¼ cup)Parmesan cheese, grated
• 30 ml (2 tablespoons)fresh parsley, finely chopped
• to tastesalt and pepper

Instructions

1. 1

   Preheat the oven

   Heat the oven to 190°C (375°F). Line a baking sheet with parchment paper and set it aside.

2. 2

   Prepare mushrooms

   Wipe the mushrooms with a damp paper towel. Remove and finely chop the stalks, setting them aside, then scrape out and discard the gills.

3. 3

   Pre-cook caps

   Arrange the mushrooms open side up on the prepared baking sheet. Bake for 15 minutes, until they release some liquid; reserve that liquid for the filling.

4. 4

   Cook the aromatics

   Set a skillet or cast-iron dish over medium heat and add the oil. Once hot, add the onion and sauté for about 2 minutes until soft. Add the garlic, chopped mushroom stalks and thyme, and cook for a further minute.

5. 5

   Wilt the spinach

   Stir in the chopped spinach and reserved mushroom liquid. Cook for 1–2 minutes, until the spinach has wilted, then take the pan off the heat.

6. 6

   Mix the filling

   Add the breadcrumbs, Gruyère and Parmesan to the pan. Season with salt and pepper, then mix until evenly combined.

7. 7

   Fill the caps

   Divide the mixture between the mushroom caps, pressing it gently into each one.

8. 8

   Bake until golden

   Bake for 15–20 minutes, until the mushrooms are tender, the cheese has melted and the tops are golden.

9. 9

   Finish and serve

   Scatter over the chopped parsley, a few extra thyme leaves and a little extra Parmesan.

What are Portobello stuffed mushrooms?

Portobello stuffed mushrooms are large mushroom caps filled and baked until tender, a familiar American-style appetiser that can also serve as a light main. Their broad caps hold a savoury mixture while bringing a substantial, earthy flavour of their own.

This version combines spinach and mushroom stalks with garlic, thyme, two cheeses and breadcrumbs. Pre-cooking the caps releases some moisture, which is then stirred into the filling for extra mushroom flavour.

Nutrition and macros by portion

The nutrition label shows one serving as written: 237 calories, 11g protein, 15g carbs, 15g fat.

The breadcrumbs supply most of the carbohydrate, while the olive oil and cheeses contribute much of the fat; the cheeses and mushrooms provide protein. Pair a cap with a generous portion of salad or other vegetables to round out the plate.

Prepare the caps first

Clean the mushrooms gently with a damp paper towel rather than soaking them. Removing the gills gives the filling a clear space and avoids adding the dark gill material to the mixture.

Keep the stalks: finely chopped, they cook with the onion and make the filling more substantial. Bake the empty caps open side up so their released liquid can be collected.

Build a balanced filling

Softened onion and briefly cooked garlic provide the savoury base, while thyme brings a fragrant note. Add the spinach only after the aromatics have cooked, and give it just enough time to wilt.

Breadcrumbs help hold the mixture together, while Gruyère melts into it and Parmesan adds a salty, savoury edge. Stir in the reserved mushroom liquid off the heat so it is distributed through the filling.

Fill without packing tightly

Divide the mixture evenly so each cap gets a similar amount. Press it down gently to help it stay in place, but avoid compressing it into a dense layer.

If the filling looks particularly wet, give it a brief stir before portioning so the breadcrumbs and cheese are evenly dispersed. The mixture should sit in the caps rather than run off their edges.

Look for the right finish

The second bake takes 15–20 minutes. The caps should feel tender, the cheese should be melted and the tops should have turned golden.

Check near the 15-minute mark, as mushroom size can affect how quickly they cook. Add the parsley and any extra thyme or Parmesan after baking for a fresh finish.

Serve as a main or side

Serve the mushrooms hot as a starter or pair them with a crisp green salad for a lighter meal. For a fuller dinner, add roasted potatoes, grains or crusty bread.

A simple, bright side works well with the rich cheese filling. If serving as part of a larger spread, cut each cap in half after baking.

Recipe notes & tips

• Reserve the liquid released during the first bake to stir into the filling.
• Chop the mushroom stalks finely so they soften quickly in the pan.
• Remove the pan from the heat before adding the cheeses and breadcrumbs.
• Divide the filling evenly for caps that cook at a similar rate.
• Check the mushrooms at 15 minutes during the final bake and continue until tender and golden.

Variations

• Use different greens: Swap the spinach for finely chopped kale and cook it until tender.
• Change the cheese: Replace the Gruyère with a similar melting cheese.
• Add chopped nuts: Stir a small handful of walnuts into the filling for crunch.
• Make it herby: Use chopped chives or oregano in place of some of the thyme.
• Add a little heat: Mix chilli flakes into the filling before stuffing the caps.

Common mistakes to avoid

• Skipping the first bake: The caps release liquid later and can make the filling watery; pre-bake them for 15 minutes.
• Washing by soaking: Mushrooms can take on excess water; wipe them clean with a damp paper towel.
• Discarding the stalks: Finely chop and cook them with the onion for extra mushroom flavour.
• Overcooking the spinach: It only needs 1–2 minutes to wilt before the pan comes off the heat.
• Packing the filling firmly: Press it into place gently so the mixture stays light.
• Baking by time alone: Check for tender caps, melted cheese and golden tops rather than relying only on the clock.

How to store

Cool leftovers, then refrigerate in an airtight container for up to 3 days. Reheat in an oven at 180°C until hot throughout; the microwave works too, though the topping may soften.

Frequently asked questions