One of my absolute favorite ingredients to work with is the carmelized onion. Nothing can compare to the sweet and savory flavor drawn out over the slow-cooking process. Carmelized onions take time (at least an hour … if a recipe says you are carmelizing onions in 15 minutes, it’s a lie!), but they are incredibly easy to make.
One problem you may encounter when making carmelized onions is that they can dry out in the long cooking process. To avoid this, begin by cooking them covered for about 20 minutes. This will draw out all of the natural moisture in the onions.
Now, you just need patience. Read a book; have a glass wine; play some Words with Friends. Just keep an eye on the onions, stirring regularly. If the onions begin scorching, reduce the heat. After another 50-60 minutes, you will have achieved carmelization.
*Pro tip: While carmelized onions are wonderful, having your house smell like onions for days is NOT. I recommend turning on the vent fan and cracking a window or door. If your oven hood doesn’t vent to the outside, you will want to open windows/doors across the room from each other for circulation. Carmelized onions will last in the refrigerator in an air-tight container for up to four days. If you are making this for guests, you can make the onions in advance and give any lingering odor time to dissipate.
Mushrooms and onions always go well together, and the thyme adds an additional depth of flavor. I am a fan of cremini mushrooms, but you could substitute white button mushrooms. You don’t need to completely brown the mushrooms as they will continue cooking in the oven.
The puff pastry is easy to prepare and work with. You find it boxed in the frozen foods section, and it thaws in just 30 minutes on the counter. True to its name, puff pastry … puffs. While that’s great for the edge of your tart, you want to poke holes over the rest of the pasty with the tines of a fork so that the center doesn’t puff. The olive oil adds some necessary moisture and helps the edges brown.
As you prepare the tart, all you really need to do is spread the ingredients evenly in layers: onions, mushrooms, then goat cheese.
I decided at the last minute to make a balsamic glaze because I felt that the tart needed just a little extra something. I am so glad I did! The sweet tartness added a perfect counterbalance to the deep and savory flavors of the other ingredients.
When making the glaze, it’s important to bring the liquid to a boil and then quickly reduce the heat. You want to glaze to thicken but still be able to drizzle it with a spoon. It’s ready when it coats a spoon and holds.
Once you take the tart out of the oven, you want to lest it rest before cutting it. This lets all of the ingredients set so that it won’t fall apart when someone picks it up. I like it best warm, but it is still good at room temperature, so it’s fine to set out on a platter for munching.
Carmelized Onion, Mushroom, and Goat Cheese Tart
Preheat oven to 425℉.
Carmelize the onions.
Add 3 T. of the butter to a Dutch oven over medium heat. When melted, add the sliced onions, sugar, and 1 tsp. of salt. Stir and cover. Cook covered for 20 minutes, stirring occasionally.
Remove the lid and continue cooking for 40 to 50 minutes, lowering the heat if the onions begin to scorch. When done, the onions should be a deep brown and have a jammy consistency.
Prepare the mushrooms.
While the onions cook, add 1 T. butter and 1 T. olive oil to a pan over medium-high heat. Add the sliced mushrooms, thyme, and pepper, and cook until softened, 5-7 minutes. Stir in the remaining ½ tsp. of salt and set aside.
Prepare the puff pastry.
Unfold the thawed puff pastry onto a sheet of parchment paper. Roll out the pastry with a rolling pin to remove creases and even out.
With a fork, poke holes all over the puff pastry leaving a small border for the crust. Brush the entire sheet with the remaining olive oil.
Build the tart.
Spread the carmelized onions over the puff pastry, leaving a small border. Spread the mushrooms evenly across (you may not use all of them). Using your fingers, drop small pieces of goat cheese all over the tart.
Move the parchment paper with tart to a baking sheet. Bake for 20-25 minutes, or until the crust is browned.
Add the balsamic vinegar and brown sugar to a small saucepan over medium-high heat. Bring to a boil. Reduce heat to medium-low and cook until sauce is thickened, 10-15 minutes. You want it to coat the back of a spoon.
Rest and serve.
When done, remove the tart from the oven and allow to rest for 5-10 minutes. Drizzle with the balsamic glaze, slice into squares, and serve.