Gruyere, Mushroom & Caramelized Onion Puff Pastry Tart

This year for Thanksgiving, I delegated more than usual. Typically I love to do most of the cooking but that said, we had two households of grandparents joining us and they all like to contribute too.

I smoked a turkey breast outside, blue cheese mashed potatoes and pretty much that was going to be it. Feeling restless that that was all I was going to do, I needed to find an appetizer, something interesting that I hadn’t done before but also, something that wasn’t going to take a ton of time or space in the oven.

Through searching around, I found something very similar to this puff pastry tart. It was super easy, the prep being able to be done the day before (important in holiday cooking land) and only take a total of about 25 minutes the next day.

Hope you enjoy my version. I can see this being adapted a thousand different ways so this might just be my master recipe that I’ll alter just about every time I make them from now on.

• 4 tablespoons salted butter, divided
• 2 tablespoons vegetable oil, divided
• 5-6 ounces crimini or button mushrooms, sliced
• 2 medium yellow onions, thinly sliced
• ¼ teaspoon dried thyme
• 1 tablespoon sugar
• 1½ tablespoon balsamic vinegar
• ¼ teaspoon garlic powder
• salt and pepper, to taste
• 4 ounces grated gruyere cheese
• 1 package (1 pound) frozen puff pastry, thawed
• 1 egg, lightly beaten

INSTRUCTIONS

In a large cast iron skillet over medium heat, heat 1 tablespoon of oil along with 1 tablespoon of butter. Add the mushrooms and sauté for about 5 minutes until tender. Remove and set aside in a medium bowl.

Heat the remaining 3 tablespoons of butter along with the 1 tablespoon of oil and sauté the onions for 5 minutes. Add the dried thyme and sugar and continue to cook for 25 minutes on medium low heat. Make sure to stir the mixture every 5 minutes or so. If the onions are caramelizing too fast, turn down the heat a little more. Add the balsamic vinegar to deglaze the pan, allow the onions to soak it all in. Turn off heat. Add the onions to the mushroom mixture. Season with the garlic powder and salt and pepper to taste, stir to combine. Allow to cool to room temperature. Mixture can be kept in an air-tight container and refrigerated for up to 48 hours at this point. Allow to come to room temperature before proceeding. Add the gruyere cheese and mix well.

Position two racks in the upper and lower thirds of the oven. Preheat the oven to 400 degrees F. Line 2 baking sheets with parchment paper or silicone mats.

Using a knife or a pizza cutter, cut the puff pastry into 2-inch squares and place them on a lined baking sheet (I used our silicone mats for this, they were perfect!). Make sure the puff pastry is cold before proceeding. If not, allow it to rest in the refrigerator for 10-15 minutes before proceeding. Using a pastry brush, brush the beaten egg on the squares. Place a tablespoon of caramelized onion mixture in the center. Bake for 20-25 minutes, rotating the pan halfway in between until crisp and golden brown. Let cool slightly before serving.

P.S. Do not open the over during the first 10 minutes of baking. This will cause the puff pastry not to…puff.

Hope you enjoy as much as I did.