What you’ll need:
- 2 frozen puff pastry sheets, about 8″ x 9″
- 2 large yellow onions
- 1 stick of butter
- 1 green apple
- ¼ cup of lemon or lime juice
- 10 ounces of crimini mushrooms
- 2 cups of Swiss cheese
- 2 cups of GruyÃ¨re cheese
- 4 (or more) cloves of fresh garlic
- Parchment paper
To start, chop the onions into thin strips that are about an inch in length and set them aside; they will carmelize more evenly if you separate the layers before putting them over heat.
Next, press the garlic and set it aside to cook with the onions and the mushrooms. Once that’s done, slice your mushrooms into thin slices.
I found it helpful to do all the prep-work before hand so that you’re ready to assemble when all the ingredients are done. In that spirit, cut the green apple so you have two quarters to work with and make fine slices; drop the slices into a little bowl and add the lemon or lime juice to keep them from turning brown. The juice will also enhance the crisp flavor of the apple.
When I made these, I used grated cheese, but I’m not convinced that was the best approach. It was hard to keep the cheese positioned on the pastry while having an adequate amount. You can use your discretion here, but I’d likely use slices next time. Once the cheese is cut or grated, it’s time to carmelize the onions.
Add half of your stick of butter and toss the onions in with half of the pressed garlic. I had never done this before, but I learned that the trick is to not let the onions sit in one spot for more than a few seconds after they start to brown and to turn the heat down to medium or a bit lower, depending on your burner and pan. Once the onions were in the pan and the heat was on, it took about 10 minutes for them to have a nice color.
Now is a good time to preheat the oven to 400 degrees and take the puff pastry sheets out of the freezer to thaw.
After the onions are nicely carmelized, set them aside and put the mushrooms in with the rest of the butter and garlic. Sautee them until they are soft and slightly browned.
When the mushrooms are done, take the pastry squares out and cut them into squares about 2″ x 3″ and place them on your parchment paper covered baking sheet. Put a layer of cheese on each square followed by the mushrooms, onions, and the apple slice. Place the baking sheet in the oven and bake for about 10 minutes until the edges of the pastry are slightly browned. Et voilÃ , you’ll have a hit appetizer that looks and tastes impressive.