Assembly

• Set aside one medium-sized mushroom for decoration, and roughly chop the rest into ¼-inch chunks.
• Heat 2 tablespoons of butter in a large saute pan over medium-high heat.
• Add the mushrooms and cook, stirring occasionally, until browned, about 7 minutes.
• Remove from heat, season with salt and transfer to a large bowl.
• Meanwhile, slice the leeks into ¼-inch strips and wash thoroughly. You should have about 3 cups of sliced leeks.
• Add the remaining 2 tablespoons butter to the now empty saute pan, and heat over medium heat.
• Add the leeks, season with salt, and cook, stirring occasionally, until they are very soft, about 10 minutes. Add them to the bowl with the mushrooms.
• Chop the asparagus stems on a ¼-inch bias, reserving the tips to decorate the top.
• Add the asparagus stems and thyme to the bowl with the mushrooms and stir to combine.
• Let cool for 15 minutes, then stir in the cheese. Season with more salt, if needed.
• On a lightly floured surface, roll the pie dough into a 13-inch round.
• Transfer it to a baking sheet lined with parchment paper.
• Add the filling and spread it over the dough, leaving a 1½-inch border.
• Fold the dough over the filling, crimping it as you go. Chill for 1 hour.
• Heat the oven to 400°F.
• Slice the reserved mushroom lengthwise into ¼ inch-thick sections.
• Brush the pie dough with egg wash and arrange the mushroom slices and asparagus tips on top of the leek filling. Arrange them very tightly and overlap them, as they will shrink in the oven.
• Brush the asparagus and mushrooms with olive oil and sprinkle with salt.
• Bake for 35-45 minutes, until the crust and vegetables have turned golden brown.
• Let cool for 20 minutes before slicing and serving. Can be served warm or at room temperature.