Rinse rice well and then soak for 30 minutes.
Preheat oven to 200˚C.
Place portabellos on a large baking tray.
Drizzle with a little olive oil and season with salt and pepper.
Roast for ± 10 minutes, depending on their size, until tender.
Remove and place on a chopping board gills side down to drain.
Heat a drizzle of olive oil in a 26cm Dutch oven.
Add the button mushrooms and cook until golden brown.
Add the onion and cook until soft.
Add the garlic and all the spices and cook until fragrant.
Scrape the mixture out of the pot and add to a bowl.
Drain the rice and add to the bowl and mix well along with 1 tsp of salt.
Off the heat - arrange the portabellos, gills down, in the pot in a well-fitting pattern.
Spoon the spiced mushroom and rice mixture over the portabellos.
Gently pour the stock into the pot.
Set a heatproof plate over the rice to keep it down.
The plate should be slightly smaller than the width of the pot. A springform tin’s base works very well for this. Cover the pot with the lid and cook on low heat for 30 minutes.
Remove the lid and check if the rice is tender.