Prepare the Shallots: In a large nonstick skillet, heat half of the butter and olive oil over medium to medium-high heat. Once hot, add the shallots and sauté, stirring occasionally, until tender and golden (about 10 minutes). Transfer them to a large bowl.

Cook the mushrooms: Increase the heat to medium-high and add the remaining butter and oil. Add the mushrooms and season with salt and pepper. Cook, stirring occasionally, for 8 to 10 minutes, until the mushrooms are golden brown.
Note: I use a 32 cm pan. If there are too many mushrooms, cook them in two batches or use two pans to ensure they brown properly.

Add the spinach: Add the spinach to the pan with the mushrooms. Stir and cook for 1 minute, just until the spinach begins to wilt. Transfer everything to the bowl with the shallots. Add the garlic and thyme, mix well, and let cool for 10 minutes.

Preheat the oven: Preheat the oven to 200°C (400°F).

Prepare the filling: Once the mixture has cooled, stir in the whole egg, the Parmesan, and the gorgonzola dolce.

Prepare the puff pastry: Unroll the puff pastry onto a baking sheet (lined with parchment paper or using the paper provided with the pastry). Spread the mushroom and spinach mixture evenly over the pastry, leaving a 3–4 cm border.
Form the edges: Brush the border with a little beaten egg yolk. Fold over the corners and sides of the pastry to create a rim. Press the corners to seal, then brush the edge with the egg yolk.

Top and bake: Sprinkle the tart with slices of red onion and dot with small spoonfuls of ricotta. Bake for 15 minutes, or until the pastry is well puffed and golden.

Serve: Serve the tart warm and enjoy!

Ingredients used in this recipe