Peel and quarter the potatoes. Put potatoes in a large pot and cover with water. Bring to a boil, reduce heat to medium-low, and simmer until tender, about 30 minutes. Drain.

Warm the cream and butter in the pot. Add potatoes, parmesan cheese, chives, and a sprinkle of salt and pepper, and mix until smooth (I used an electric mixer).

Thinly slice the onion. Heat 1/2 TBSP of olive oil in a skillet over medium heat, then add onions. Cook until browned, about 20 minutes.

Meanwhile, preheat oven to 375. Coat a baking sheet with cooking spray, and set portobello mushrooms gill-side up on the baking sheet. Drizzle with 1/2 TBSP of olive oil, and roast for about 25 minutes, or until tender. Cool, then thinly slice.

During this time, chop the crimini mushrooms. In a bowl, toss with 1 TBSP of olive oil, salt and pepper. Spread out on a baking sheet and roast until tender, about 20 minutes. Cool, then toss with the asiago cheese, onions, thyme and oregano.

Coat a 9-inch deep-dish pie plate with baking spray. Layer portobello slices on the bottom. Add half of the crimini mushroom mix as a second layer, then spread about 1/3 of the potatoes on top. Add the remaining crimini mixture, then top with the remaining potatoes. Sprinkle a pinch of asiago cheese to top it off.

Bake until golden, around 30 minutes. Let it cool, then slice and enjoy.