1. Preheat the oven to 375°F. Line the bottom of a 10-inch tart pan with parchment paper.

2. Roll the puff pastry into a 14-by-14-inch square so it can fully cover the bottom and sides of the pan.

3. Fit the pastry into the tart pan and trim the edges. Freeze the lined pan while preparing the filling.

4. Warm the butter and oil in a medium skillet over medium heat. Add the onion and cook for 5–6 minutes until softened.

5. Add the mushrooms and cook for another 5–7 minutes, allowing them to release their moisture.

6. Stir in the chicken, walnuts, rosemary, and garlic. Cook until the mixture is mostly dry.

7. Add the water or grape juice and cook until the liquid reduces again. Season to taste with salt and pepper.

8. Cool the filling completely. For quicker cooling, spread it on a parchment-lined baking sheet and chill for about 5 minutes.

9. In a bowl, beat together the cream cheese, eggs, orange zest, salt, and white pepper until smooth.

10. Remove the pastry from the freezer and fill it with the cooled chicken–mushroom mixture.

11. Spread the cream cheese topping evenly over the surface.

12. Bake for 30–35 minutes, or until the top is lightly browned and set.

13. Let the tart cool slightly before slicing. Serve warm or cold.