Ingredients

For the crust:
• 1 cup plus 2 tablespoons all-purpose flour
• ¼ cup yellow cornmeal
• ¼ teaspoon salt
• 6 tablespoons unsalted butter, cold and cut into ½ inch pieces
• 1 large egg
For the filling:
• 1 tablespoon olive oil
• 1 tablespoon unsalted butter
• 2 medium shallots, thinly sliced
• 1 clove garlic, minced
• 1 teaspoon chopped fresh thyme
• ½ pound cremini mushrooms, thinly sliced
• 1 pound assorted wild mushrooms (such as shiitake or oyster), torn into small pieces*
• 1 teaspoon salt, divided
• freshly ground pepper, to taste
• ¼ cup mascarpone cheese, room temperature
• ¼ cup milk
• 2 large eggs
• ½ cup freshly grated gruyere cheese
• ¼ cup freshly grated parmesan cheese

Instructions

1. To make the crust - add the flour, cornmeal and salt to the bowl of a food processor. Add in the butter. Pulse until the butter is the size of tiny peas. Add the egg and process until the dough starts to clump together (it will look like wet sand). Dump the dough onto a floured surface and use your hands to bring it together. Roll out the dough to a 12-inch circle (rolling out the dough between two pieces of plastic wrap made this very easy). Transfer the dough to a 9-inch tart pan and press the dough against the bottom and sides. Remove the excess dough from the top. Place the tart pan on a baking sheet and put in the freezer until firm, about 30 minutes.
2. Preheat the oven to 375 degrees. Lightly butter one side of a 12-inch square of aluminum foil. Press the foil firmly against the bottom and sides of the crust (butter side down). Bake for 10 minutes (no pie weights needed). Carefully remove the foil and then bake for another 5 to 8 minutes, until lightly golden brown around the edges. Place on a wire rack. Reduce the oven temperature to 350 degrees.
3. To make the filling - set a large skillet over medium heat. Add the olive oil and butter. When the butter is melted, add the shallots. Cook, stirring occasionally, for about 2 to 3 minutes, until soft. Add in the garlic and thyme and cook for 30 seconds, until fragrant. Increase the heat to medium high and add in the mushrooms (if the mushrooms won’t all fit in your skillet, add as many as you can and as they cook down you’ll be able to add more to the pan). Cook for about 9 to 10 minutes, stirring occasionally, until the mushrooms are tender and the liquid has evaporated. Stir in ½ teaspoon salt and pepper (to taste). Transfer to a plate to cool.
4. In a medium bowl, add the mascarpone. Slowly pour in the milk and whisk until the mixture is smooth. Whisk in the eggs. Add in the gruyere, parmesan and remaining ½ teaspoon salt. Add in the cooled mushrooms and mix to combine.
5. Carefully pour the mixture into the tart shell. Bake for 35 to 40 minutes, until slightly puffed and lightly golden brown on the top (if you insert the tip of a small knife into the center, it should not release any wet custard). Let the tart cool for at least 10 minutes before removing from the pan to serve. Serve warm or at room temperature.

Notes