1 ½ lbs assorted mushrooms, sliced (chanterelles, crimini, shiitake, oyster)
1 large shallot
A few sprigs fresh thyme
3 tbsp butter
2 tbsp olive oil
1 tsp white wine vinegar
1 cup gruyere, shredded
¼ cup parmesan
2 puff pastry sheets
Salt and pepper
Heat a large pan on medium-high. Once hot, add olive oil and shallots. Cook until lightly browned. Add the butter. When it becomes foamy, add the mushrooms and thyme and sauté until most of the moisture has evaporated and they have reduced in size. Add white wine vinegar and season with salt and pepper. Set aside to slightly cool.
Preheat oven to 375°F. Line two baking trays with Silpat or parchment paper.
Slightly roll out puff pastry sheets to form a rectangle. Cut each sheet into 4 equal pieces to form 8 mini sheets. Use a paring knife to score a border ¼ inch from the edges of each rectangle. Do not slice all the way through. Brush the edges with egg wash.
Equally distribute and sprinkle gruyere onto each sheet, making sure to avoid the edges. Top with the mushrooms. Finish with a sprinkle of parmesan over the top.
Bake for 25-30 minutes, or until the edges are golden brown and the cheese is bubbly.