Easy Tart with Caramelized Onions, Mushrooms & Gruyère

When it comes to pulling together an easy appetizer I often turn to my trusty filo dough to whip up something classically Greek, like spanakopitakia or feta-stuffed filo cigars.  While they require a little planning, nevertheless, I know they will always turn out well and that they will disappear very quickly.  Because they are so easy and popular, I am always on the lookout for something different to use as a base for delicious toppings.

Recently I spotted an almost forgotten package of puff pastry in the freezer and wanted to experiment with it to see what I could come up with for an easy appetizer. I gathered a few ingredients that I had on hand that I thought would make a tasty topping:  a few onions, a package of Cremini mushrooms, two small potatoes, and some Gruyère cheese.

The first step for this recipe is to caramelize the sliced onions, low and slow, until they become sweet and golden brown.  Next, I dry-sauté the mushrooms until they release all their moisture and then I cook them in olive oil with some fresh thyme. Those ingredients alone would have made a great topping, but I thought that adding a couple of very thinly sliced potatoes would make this an even more substantial appetizer or light lunch, so added those too along with some crushed fennel seeds.

Once the topping cooled off, I rolled out the puff pastry and topped it with the caramelized onions, mushrooms and sliced potatoes. I spread some cheese over it and put it in the preheated oven.

Easy tart with caramelized onions ready for the oven

I baked the tart until the puff pastry became golden, crispy and all puffed up. The only difficult part about this recipe is to wait for it to cool down. Thankfully this does not take long at all, at which point you can cut it into small squares and pass it around to your guests.  With Memorial Day coming up this weekend, this foolproof appetizer might be the star of your backyard gathering or any future outdoor entertaining this summer!

5.0 from 1 reviews

Easy Tart with Caramelized Onions, Mushrooms and Gruyère

 

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A savory tart topped with sweet caramelized onions and mushrooms and cut into appetizer-size pieces.

Author: Marilena Leavitt

Recipe type: Appetizer

Serves: 20 pieces

Ingredients

• 1 TBSP. olive oil
• 1 TBSP. butter
• 2 med. yellow and/or red onions, thinly sliced
• ½ TBSP. brown sugar
• 2 TBSPS. Balsamic vinegar
• --- --- sea salt & freshly ground pepper
• 8 oz. Cremini mushrooms, cleaned and thinly sliced
• 1 TBSP. fresh thyme
• 2 sm. Yukon Gold potatoes, thinly sliced
• 1 tsp. fennel seeds, toasted and crushed (optional)
• --- --- sea salt & freshly ground pepper
• 1 sheet frozen puff pastry (½ of a 17oz. package)
• (defrosted & thawed according to directions on package)
• 4 oz. Gruyère cheese, grated

Instructions

1. 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.
2. 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.
3. 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.
4. 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).
5. 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.

Notes

1. If you wish, you can make an egg wash with one egg and one tablespoon of water, and brush it around the edges of the tart before baking.

2. Using one sheet of puff pastry, you can also form 6 individual tartlets, round or square.

3.5.3240

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