Place the forest mushrooms and morels in two small separate bowls and pour in just enough warm water to cover them. Set aside for a half hour to soften. Drain, reserve the water, and drain it through a fine mesh sieve or cheesecloth to trap any dirt or sand.

Rinse the portobellos and field mushrooms quickly under cold water and pat dry. Alternatively, wipe them clean with a damp towel, without rinsing at all (it’s actually better not to rinse them). Chop.

Heat the olive oil and butter in a large pot and sauté shallots, garlic, parsley and thyme for two minutes, stirring. Add the portobellos and field mushrooms and stir to coat. Add the porcini and morels. Stir. Pour in the wine, raise the heat and as soon as the wine steams up, add the broth and strained mushroom water. Bring to a boil, season with salt and pepper, reduce heat to medium and simmer for 7-8 minutes, until the mushrooms are tender.

Using a slotted spoon, remove about half of the solid contents of the soup and puree in a food processor until smooth. Return to the pot and heat. Whisk the yogurt, cream and flour together, and add to the pot. Stir gently. Cook for another few minutes until the soup thickens slightly. Serve.