Puree ricotta in a food processor until smooth, about 1 minute.

Add 1 egg yolk and 2 teaspoons of olive oil to the ricotta and blend until combined.

Transfer the ricotta mixture to a bowl and fold in the creme fraiche or sour cream.

Heat the remaining 2 tablespoons of olive oil in a heavy skillet over medium-high heat.

Add the sliced wild mushrooms and sauté for 7 minutes, stirring occasionally.

Mix in the fresh thyme leaves and season with salt and pepper to taste.

Add the butter to the mushroom mixture and sauté until the mushrooms are tender, about 4 minutes longer.

Mix in the thinly sliced green onions.

Preheat oven to 400°F (200°C).

Roll out the thawed puff pastry on a lightly floured surface to a 13x9-inch rectangle.

Using a sharp knife, score a line around the entire perimeter of the dough, 1/4 inch in from the edge, cutting halfway through.

Brush the 1/4-inch dough border with the egg yolk glaze (1 egg yolk beaten with 1 teaspoon of water).

Transfer the prepared dough to an ungreased heavy baking sheet.

Spread the ricotta mixture evenly over the dough, inside the scored border.

Top the ricotta mixture with half of the sautéed mushrooms, then half of the thinly sliced Gruyere cheese.

Add the remaining mushrooms and Gruyere cheese.

Bake the tart in the preheated oven until the crust is golden and the Gruyere melts, about 25 minutes.

While the tart bakes, toss the fresh Italian parsley leaves, fresh chives, fresh tarragon leaves, and fresh chervil leaves with olive oil and lemon juice in a small bowl.

Season the herb salad with salt and pepper.

Once the tart is baked, cut it into rectangles.

Transfer the tart rectangles to plates.

Garnish each serving with the fresh herb salad.