Chop the cauliflower into roughly equal sized pieces and add to a large saucepan. Cover with water and bring to a boil. Season with salt and cook the cauliflower until tender. Drain.
Place a large frying pan over a medium heat. Add the olive oil, onion, carrots and celery. Cook until slightly golden and caramelised. Add the mushrooms in 6 parts, making sure each batch is cooked before adding the next.
Remove the wild mushrooms from the boiling water, reserving the water, and roughly chop. Add to the mushrooms along with the tomato paste. Increase the heat to medium-high and add the red wine. Cook until the red wine has almost evaporated before adding the mushroom soaking liquid and vegetable stock. Reduce the heat to low and simmer for 5 to 10 minutes or until roughly half of the liquid has been absorbed. Remove from the heat.
Place the cauliflower in a food processor or high powered blender along with 2 tbs olive oil, the nutritional yeast, mustard, salt and thyme leaves. Blend until smooth and taste. Adjust seasonings as required and add the nutmeg and blend for a further minute.
Divide the mushrooms between 4 large ramekins and top with the cauliflower mash. Bake for 20 minutes or until lightly golden.
Nutritional Yeast (sometimes called savoury yeast flakes) is available in health food stores. Make sure you purchase nutritional yeast and NOT brewers yeast as they are very different things. You can also purchase nutritional yeast online from amazon (see link in recipe) as well as in Australia from here.