Place the porcini mushrooms in a small bowl and pour the boiling water over them. Set aside.
Heat the olive oil in a large dutch oven or stockpot over med-high heat. Add the shallots and saute until translucent, about two minutes. Add the chopped portabella and button mushrooms continuing to cook until softened. Stir in the garlic, thyme, herbs de provence and bay leaf and cook for an additional 1 minute.
Remove the porcini mushrooms from the water and roughly chop. Add the mushrooms and the mushroom infused water to the pot along with the salt and pepper stirring to combine.
Add the broth to the mixture and bring to a boil.
While the broth is coming to a boil, combine the milk, yogurt and cornstarch in the bowl of a mini food processor. Blend on low until thoroughly combined. You can also whisk in a small bowl by hand, just be sure the mixture is smooth and has no lumps.
Add the milk/yogurt mixture to the pot and turn the heat down to med-low. Stir the soup constantly until the mixture begins to thicken. Approximately 4-5 minutes.
Stir in the chopped parsley and serve immediately. You can top each serving with additional parsley or grated parmesan cheese.