准备

• Preheat the oven to 425°F. In a glass liquid measure or glass jar, combine 6 Tbs. of the olive oil, the vinegar, the honey, 2 tsp. of the rosemary, the garlic, and 1/2 tsp salt. Whisk or shake well to combine.
• Rub a shallow 11-by-7-inch baking dish with olive oil and combine the grapes and the shallots and season with a big pinch of salt. Rub a 13-by-9-inch baking dish with olive oil and arrange the portobello caps, stem-side up, in a single layer and season each cap with a pinch of salt. Pour 1 Tbs. of the dressing inside and around the edges of each of the mushroom caps (for a total of 4 Tbs.). Let the mushrooms marinate for 20 minutes.
• 毛毛雨2汤匙。在葡萄和葱上的调味料，然后折腾。（保留剩余的敷料。）烤葡萄和葱，搅拌一次或两次，直至柔软变褐色，约40分钟。（锅底的液体将有些糖浆。）
• Meanwhile, fill a large pasta pot three-quarters full of water and bring to a boil. Rinse the farro in a colander. Add 1 tsp. salt and the farro to the boiling water and cook at a rapid simmer or low boil, partially covered, until the grains are tender (they will look “popped”), about 30 minutes. Drain in a colander, return to the pot (off the heat), and cover to keep warm.
• 当葡萄和葱烘烤20分钟时，将Portobello帽放在烤箱中，烘烤20分钟。（蘑菇的边缘可能已经扁平；它们会损失一些体积；液体可能在它们的顶部冒泡。底部也将是棕色的，并且会煮熟。）
• Transfer each of the mushroom caps, keeping them stem-side up, to an individual warm plate or a warm platter. (If there are any juices remaining in the pan, drizzle them over the mushrooms.) Transfer the farro to a medium mixing bowl and season it with 1/4 tsp. salt. Stir in the roasted grapes and shallots (be sure to scrape out all of the pan juices), the remaining 1 tsp. rosemary, and 1 to 2 Tbs. of the remaining dressing. Taste and season with more salt, if necessary. Spoon the mixture evenly over each of the mushrooms. (For a nicer presentation, use a smaller amount of the farro mixture and mound it completely in the center of the mushroom with just the edges of the mushroom peeking out and the rosemary sprig leaning against the mound. You’ll have extra farro, but it reheats well.) Garnish each serving with a rosemary sprig and serve right away.