Inspired by a heavier version I shared as an appetizer while out with some girlfriends. In a time when everyone seems to be trying to "lighten up", I find one stuffed portobello mushroom with some veggies and a great salad to be a perfect serving size and entirely satisfying.
Heat 1/2 cup of olive oil in heavy large skillet over medium-high heat. Add onion, basil, garlic, and rosemary. SautÃÃÃ‚Â‚ÂÃ‚ÂƒÂ© until onion softens, about 5 minutes. Transfer to large bowl; mix in shrimp, crab, 1 1/3 cup panko breadcrumbs, Parmesan cheese, and mayonnaise. Season filling to taste with salt and pepper. Set aside. Break off mushroom stems. Using a spoon, carefully scrape dark gills out of the inside of the mushrooms. In a small bowl, break egg and add a bit of water to make an egg wash. Dip round side of Portobello mushrooms into egg wash, then press onto plate with remaining 1/3 cup panko breadcrumbs so you end up with a light coating of breadcrumbs on the mushroom. Using the same pan you just sautÃÃÃ‚Â‚ÂÃ‚ÂƒÂ©ed the onion mixture in, and adding a bit more olive oil to the pan, fry mushrooms breadcumb side down just until the panko is lightly browned, about 3-5 minutes. Arrange mushrooms, rounded side down, in baking dish or on a heavy sheet pan. Mound crab/shrimp filling into cleaned inside of mushrooms, pressing filling to compact slightly. (Can be made 6 hours ahead. Cover and refrigerate if making ahead.) Preheat oven to 350ÃÃÃ‚Â‚ÂÃ‚Â‚Â°F. Combine mozzarella and asiago cheese. Sprinkle mushrooms with the cheese mixture and bake until tender and filling begins to brown, about 35 minutes. Serve hot.