Vegetarian Chicken-Fried Portobello Mushroom Steaks

1. Position an oven rack at the top of the oven, and preheat the broiler. Arrange the mushrooms on a baking sheet, and broil until the sides facing up begin to soften, about 5 minutes. Flip, and continue to broil until the sides facing up are soft, about 5 minutes more. Let cool.
2. Put the mushrooms, gill-side up, between 2 pieces of plastic wrap, and pound to about 1/4 inch thick with a meat mallet. Season all over with 1/2 teaspoon salt.
3. Whisk together the flour, baking powder and 1 teaspoon each salt and pepper in a shallow dish. Whisk together the milk and eggs in a separate shallow dish.
4. Lower the oven heat to 250 degrees F. Put a rack over a rimmed baking sheet. Heat about an inch of oil to 350 degrees F in a large cast-iron skillet or Dutch oven over medium-high heat.
5. While the oil heats, dredge each mushroom in the flour mixture to completely coat; shake off any excess. Then dip into the egg mixture until fully coated; let the excess drip off. Return the mushroom to the flour mixture, and dredge a second time, until completely coated, pressing firmly into the flour mixture. Arrange on one side of the rack on the baking sheet.
6. Add 2 of the breaded mushrooms to the hot oil, and cook, turning once, until crisp and golden, about 5 minutes total. Transfer the mushrooms to the unused side of the rack. When the oil comes back to temperature, repeat with the remaining 2 mushrooms and keep the first 2 warm in the oven.
7. Serve the mushroom steaks with mashed potatoes and generous spoonfuls of hot gravy. Garnish with chives or scallions if using.

Vegetarian Gravy:

1. Position an oven rack in the top position in the oven and preheat to 450 degrees F. Toss the onions, celery, carrots and garlic with the oil and 1 teaspoon salt on a rimmed baking sheet. Roast until the vegetables are charred in some places, 25 to 30 minutes.
2. Bring the roasted vegetables, 1 cup water, mushrooms, thyme, sun-dried tomatoes, soy sauce, bay leaf and 1 teaspoon salt to a simmer in a medium saucepan over medium-high heat. Cook, stirring occasionally, until most of the liquid is gone, 8 to 10 minutes. Add 6 cups water and 1/2 teaspoon salt, and bring back to a simmer. Reduce the heat to medium-low, and gently simmer until reduced by about one third, about 45 minutes. Strain the stock into a large liquid measuring cup, then squeeze all the liquid out of the solids with the back of a ladle (there should be about 4 cups of stock); discard the solids. (If not making gravy right away, let the stock cool to room temperature, then refrigerate for up to 3 days or freeze for up to 1 month; warm slightly before making gravy.)
3. Melt the butter in a medium saucepan over medium heat. Add the sage leaves to the butter, and stir for 30 seconds; remove the fried sage leaves, and set aside. Add the flour to the saucepan, and stir until smooth and lightly golden, about 2 minutes. Slowly pour in the warm stock while whisking constantly until smooth and thick, 8 to 10 minutes.
4. Chop the fried sage, stir it and the parsley into the gravy and season to taste with pepper.