In a food processor, finely chop the mushrooms. Place in a bowl and sprinkle with the lemon juice to prevent the mushrooms from discoloring.

In a saute pan, heat 1 tablespoon of butter. When the butter is melted, saute the shallots and garlic. Add the mushrooms and season with salt and pepper. Saute for 3 to 4 minutes. Drain the mushrooms in a sieve placed over a saucepan, and reserve this liquid. Place the mushrooms in to another saucepan, and cook over high heat until all the excess moisture has evaporated.

Combine the cream and yolks in a small mixing bowl, and whisk until blended. Whisk this mixture into the mushrooms and let cook over high heat for 2 minutes. Remove from heat and allow to cool.

Gently open out the petals of each blossom and fill the center of each with 1/2 tablespoon of the mushroom mixture. Nestle a truffle in the center of each blossom and carefully close the petals up around the truffle and stuffing. Place the zucchini on the wire rack or bamboo steamer that fits over a shallow saute pan. Cover with a sheet of aluminum foil.

Pour water about halfway up a shallow saute pan and bring to a boil over high heat. When water is boiling, place the covered rack with the zucchini on top of the pan. Steam for 15 minutes, or until the zucchini is fork tender. In a small saute pan, reduce the reserved mushroom liquid to 2 tablespoons of liquid. Cut the remaining butter into cubes and whisk into the mushroom liquid, until each cube is incorporated. Season with salt and pepper. Spread the spinach leaves on the platter. Place the zucchinis on top of the spinach, and drizzle with the sauce. Garnish with the chervil sprigs.