Braised Portobello Mushroom Caps

This is another PDX-inspired dish, this time an homage to the delicious and eponymous "steak" I had at Portobello, Portland's Italian vegan restaurant (we also ordered a Caesar salad, some sort of boozy parfait, and the most amazing gnocchi with summer vegetables and mint, the last of which I may attempt at some future date). Their portobellos are served grilled, and artfully presented atop a round of crispy polenta with a side of sautéed greens and a drizzle of balsamic. For my own, more homespun version, I first marinated the bejesus out of the mushroom caps, then opted for an approach more like braising, which reduced the marinade into a nice glaze/sauce. On the whole, I have to admit that these turned out really well - the only downside being that they were gobbled up so quickly that there were hardly any leftovers! (Note to self: next time double the recipe.)

Braised Portobello Mushroom Caps
Ingredients
~ 6 large portobello mushroom caps, stems removed
~ 2 cups vegetable broth
~ 2 tbsp. balsamic vinegar
~ 1 tbsp. each: agave syrup, vegan Worcestershire sauce
~ 1 tsp. each: Liquid Smoke, Marmite, prepared mustard
~ 1 tsp. each: marjoram, thyme, smoked paprika, garlic powder
~ 1 tbsp. olive oil
~ 1 small red onion, diced fine
~ 2 tbsp. minced garlic

Directions
~ In a bowl or beaker, whisk together everything from the broth through the garlic powder.
~ Arrange the mushroom caps in a large, shallow casserole, gill side up. Pour the marinade over them, then spoon as much of it as possible into the mushroom cavities. Cover with foil or plastic wrap and refrigerate for as long as possible (I put mine in at noon to cook for that night's dinner).
~ Turn the oven to 350 fahrenheit, coat a rimmed baking dish with cooking spray, and place the dish in the oven.
~ In a skillet, heat the oil over medium heat and sauté the onions and garlic for about 3 minutes; until just fragrant.
~ Add 3 of the portobello caps and half of the marinade; cover the skillet and cook 5-7 minutes.
~ Raise the heat to medium-high, uncover the skillet, and turn the caps over. Continue to cook uncovered for another 5-7 minutes, basting frequently with the marinade, which should reduce a bit during this process.
~ Transfer the cooked mushroom caps and any remaining liquid to the (eagerly waiting) baking dish, and repeat with the remaining mushrooms and marinade.
~ Serve hot over mashed potatoes, pasta, rice, or - best of all! - soft or crispy polenta, drizzled with the marinade/sauce, with some garlicky greens and a beautiful salad on the side.