Mushroom, Caramelized Onion and Potato Tart

5 from 4 votes

Mushroom, Caramelized Onion and Potato Tart

This savory Mushroom, Caramelized Onion, and Mashed Potato Tart (or pie or galette) has a flaky pie crust that gets filled with mashed potatoes, goat cheese, golden brown mushrooms and flavorful caramelized onions. Baked and topped with fresh thyme, this rustic pie is perfect as a meal, side, or appetizer.

Prep Time30

Cook Time45

Total Time1 15

Course: Appetizer, Main Course, Side Dish

Cuisine: American, French

Servings:

Calories: 165kcal

Author: Callan Wenner

Equipment

Rolling Pin
10" cast iron skillet or large baking sheet
Pastry brush for egg wash

Ingredients

1 disc pie dough using this all-butter pie crust
2 large yellow onions peeled and thinly sliced
½ tablespoon extra virgin olive oil
2 russet potatoes peeled and evenly chopped
2 tablespoons salted butter 28g
¼ cup sour cream 57g
2 tablespoons milk 30ml
½ teaspoon kosher salt
¼ teaspoon black pepper
8 oz mushrooms of choice quartered or roughly chopped
1 tablespoon olive oil
2-4 oz goat cheese
2 sprigs fresh thyme
1 egg for egg wash

Instructions

Pie Dough

Make the all-butter pie crust following recipe instructions and hydrate in the fridge for 2 hours.

Caramelized Onions

Remove the onion peels and thinly slice each onion, discarding the root.
Heat a large skillet over medium high heat and add the olive oil. Then, add the sliced onions and toss to coat.
Reduce the heat to low and stir occasionally. The onions will begin to get translucent, then start to gain color, then turn to a nice caramelized color and texture.
Increase or decrease the heat, as needed, taking care not to burn the onions. This takes about an hour. Transfer to a bowl to cool.

Mushrooms

Clean and quarter the mushrooms. Then, heat a large pan over medium high heat and let it get very hot. Add the olive oil and mushrooms and toss to coat, then spread them evenly in the pan.
Allow the mushrooms to cook for about a minute, then toss. Cook until browned and any liquid released has cooked off. Transfer to a bowl to cool.

Mashed Potatoes

Add water to a large pot and bring it to a boil. Peel and chop the potatoes into even pieces, about 2" chunks.
Once boiling, salt the water liberally, then add the potatoes. Cook for 15-20 minutes, or until a sharp knife inserts into the center of the potatoes without any give.
Drain, then add back to the pot over low heat. Partially mash the potatoes, then add the butter, sour cream, milk, salt and pepper and continue mashing until smooth. Transfer to a bowl to cool.

Assembly

Preheat the oven to 375℉/190℃ and parchment line a cast iron pan or large cookie sheet.
Lightly flour your work surface and roll out the pie dough until it's between ⅛-¼" thick, then drape it into the cast iron pan (or place on a sheet pan).
Spread the mashed potatoes evenly into the center (meeting the edges of the cast iron), leaving 2-3" of the dough bare. Sprinkle the goat cheese on top of the mashed potatoes, followed by the mushrooms, caramelized onions, and thyme leaves.
Fold the excess pieces of pie dough in towards the center in 4-5 sections, gently pressing down.
Whisk together the egg and water, then brush it completely over the top of the pie dough.
Bake the tart for 45-55 minutes until the crust is golden in color. Remove from the oven and cool for about 15 minutes, then slice and enjoy!

Notes

Store the tart covered in the fridge for 3-5 days. Reheat in the microwave or a 350℉ oven until the potatoes are warmed through.

I do not suggest using store bough pie dough for this. The homemade dough produces a larger crust, which is necessary to hold all of the ingredients.

Caramelized onions: be patient with this process and keep the heat relatively low. If the onions begin to burn at all, lower the heat and add in a tablespoon of water. Stir occasionally, but not too often

Use your fingers to pull apart the caramelized onions to spread them evenly on top of the tart.

Nutrition