Step 1

Clean and finely chop the portobello mushrooms into very small pieces.

Step 2

Heat oil and butter together in a frying pan over medium heat, and when it's hot, add the mushrooms with a large pinch of salt.

Step 3

Cook the mushrooms, stirring frequently, until they darken and reduce in size. Keep cooking for 5-10 minutes on low heat to help them evaporate as much of their moisture content as possible. Remove from the heat and allow to cool completely.

Step 4

Once the mushrooms have cooled, place them into a large mixing bowl.

Step 5

Grate the onion and garlic into the bowl with the cooked mushrooms. Then add the egg, fresh parsley, dried thyme, lemon zest, lemon juice, and breadcrumbs.

Step 6

Use a large spoon to thoroughly mix everything together, and season with salt and pepper.

Step 7

Preheat the oven to 150℃/300℉ and grease an oven dish with butter.

Step 8

Portion the mushroom stuffing into six even-sized balls by rolling/squeezing it in your hands. Place the stuffing balls into the dish and add a small piece of butter on top of each one. Sprinkle with salt and pepper.

Step 9

Bake the walnut and portobello mushroom stuffing balls for one hour.