MF: Made these for dinner with Jane. I added pancetta but made it pretty salty. Use less or omit.

Preheat oven to 400 degrees F and line two baking sheets with parchment paper.

Heat the olive oil in a wide, heavy-bottomed pan over medium-low heat and add the onions. Cook, stirring occasionally, until they are well caramelized, 20 minutes or more. Add vinegar near end. Add the garlic and the thyme and saute until fragrant, about 1 minute. Season with salt and pepper to taste. Set aside.

Add the butter to the pan. Once melted, add the mushrooms and saute, stirring occasionally, until they are completely soft and all of the liquid evaporates, about 20 minutes.

Add the wine, scraping the bottom of the pan to pull up all of the browned bits, and cook until all of the liquid has evaporated. Remove from heat.

Working with frozen puff pastry and cut out 2-1/2 circles with biscuit cutter and placie them on the baking sheets. Using a 1-1/2 biscuit cutter, gently press in the middle of the larger circles just until scored, but not cut through. This makes a 1/2 border that will puff up around the filling. Roll left-over pieces and make a couple more if desired.

Brush the edges of the dough rounds with the egg wash. Top the rounds of puff pastry with a small spoonful of the onion and mushroom mixture, trying to keep the filling within the score marks. Top with the shredded Gruyere cheese.

Bake until the pastry is golden brown, about 15 to 25 minutes. Garnish with fresh chopped parsley.