Make the croutons first. Preheat the oven to 180 degrees C, 356 F I use a fan assisted electric oven, please adjust according to your own oven.
Heat the oil in a skillet over a medium to high heat. Add the garlic and thyme leaves, cook for about 2 minutes then remove the garlic. Carefully transfer the oil to a large bowl then add the bread. Mix with a large spoon so the bread is lightly coated in the oil. Spread the bread out on a baking tray and bake in the middle of the oven for 8 minutes.Remove the tray from the oven then sprinkle the parmesan over the croutons, toss the croutons a little then return to the oven and bake for another 5 minutes. They should be crispy and golden brown. Remove from the oven sprinkle with the sea salt and leave to cool.Keep any leftover croutons in an airtight container and use within a week.
While the croutons are baking start making the soup. Melt the butter in a large saucepan, add the onion and gently cook for about 5 minutes until the onion is soft. Add the garlic and cook for 1 minute. Then add the mushrooms, thyme, nutmeg, salt and black pepper, turn up the heat to medium hot and cook the mushrooms for about 10 minutes until they release all their juicy goodness.
Now sprinkle the mushrooms with the flour and add the stock, stir then leave to simmer for about 10 minutes. Test the seasoning and add more pepper if you need it. Remove the thyme sprig when the soup has thickened slightly then turn off the heat and blend the soup with a hand blender.
Once the soup is smooth return it to the heat, add the cream and bring the soup to a fast simmer. Serve immediately with the croutons.