Wash and dry potatoes. Thinly cut into ¼-inch slices. You can use a mandolin to ensure even slicing. Thinly slice onion and set aside.

Heat mushroom-infused olive oil in an 8-inch oven-safe skillet. Once heated, fry potato slices in single-layer batches, until browned but still soft. Drain potatoes on a paper towel-lined plate and continue until all potatoes are cooked.

Remove all but 1 tablespoon oil from the skillet and cook sliced onion for 3 to 5 minutes, until translucent.

Spread the onions evenly around the bottom of the skillet and layer on potato slices, overlaying in a circular pattern from the outside in, until the onions are covered with a single layer. Sprinkle on about ¼ teaspoon fine sea salt.

Repeat with a second layer of potatoes, until all potatoes are in the skillet, seasoning with another ¼ teaspoon fine sea salt on each layer. You should end up with 2 to 3 layers of potato.

Add 6 eggs, 1 teaspoon water and ½ teaspoon fine sea salt to a large bowl and whisk until well combined. Slowly and evenly pour the egg mixture into the skillet, over medium heat.

Shake the skillet to ensure even distribution of the eggs. Once eggs are starting to set on the edges, use a spatula to gently lift around the edges, ensuring more egg liquid is distributed on the bottom of the pan.

Place skillet in the oven, under the broiler, and bake for 3 to 5 minutes, until the top begins to brown and eggs are completely set. Use a towel or pot holder to remove the pan from the oven, and sit on the stovetop to cool for about 5 minutes.

Once slightly cooled, place a plate over the top of the skillet and carefully flip over to release the tortilla from the skillet.

Cut into slices and serve with crispy mushrooms to garnish, as desired. Leftovers store well for up to 3 days in the refrigerator.