EASY TART WITH CARAMELIZED ONIONS, MUSHROOMS AND GRUYèRE

Steps:

• Heat a large saucepan over medium-high heat. When the pan is hot, add the olive oil and the butter together, followed by the sliced onions. Cook for about 10 minutes or until the onions wilt and start to brown. At that point add the next three ingredients (sugar, vinegar, salt and pepper). Reduce the heat and cook gently, uncovered for about 20 more minutes or until the onions are completely caramelized. Add a little water if the onions look like they are drying out. Taste and adjust the seasoning. Remove the onions to a separate bowl.
• Add the sliced mushrooms to the same pot and sauté (without oil) for a few minutes until they release their moisture. At that point, add a little olive oil and the thyme leaves and cook for a few minutes, stirring frequently. Once the mushrooms start lightly brown, add the sliced potatoes and the fennel seeds. Season everything with some salt and pepper and cook for a few more minutes, until the potatoes soften a little. Set the mixture aside to cool.
• Unfold the thawed sheet of puff pastry and place it on a work surface. Roll it out into a 10"x14" rectangle and remove it to a baking sheet lined with parchment paper. Prick with a fork every few inches to prevent the pastry from bubbling while it bakes. Using a very sharp knife, score the perimeter of the dough about ¼- to ½-inch from the edge.
• Spread the cooled onions evenly over the puff pastry. Top with the sautéed mushrooms and potatoes and sprinkle with the Gruyère cheese. (Refrigerate if not baking immediately).
• Preheat the oven to 375°F. Bake the puff pastry on the middle rack for 25-30 minutes or until the cheese is bubbling and crust is nice and golden. Allow the tart to cool for 10 minutes then cut it into 20 little rectangles. Serve warm or at room temperature.