2. Peel the onions. Trim the root ends so they will stand upright, and remove 1/2 inch from the tops. Rub 1 1/4 teaspoons of the oil over each onion and season with 1/8 teaspoon of the salt and a pinch of the pepper. Place on the baking sheet and roast until tender and caramelized around the edges, about 45 minutes. Remove from the oven and let cool slightly. Leave the oven on.
3. When the onions are cool enough to handle, push out the centers, leaving a shell. Return a piece of the center to each to form a bottom. Chop the remaining centers.
4. In a bowl, combine the mascarpone, thyme, garlic, shallots, and the remaining 1/2 teaspoon salt and 1/4 teaspoon pepper and mix until blended. Stuff the onions in the baking dish with the cheese mixture.
5. Bake until the onions are warmed through and the cheese has melted completely, 5 to 6 minutes. Remove from the oven and transfer to serving plates. Place 1 thyme sprig in the center of each onion, and serve immediately, with a spoonful of the onion pieces alongside.
Adapted from From Emeril's Kitchen: Favorite Recipes from Emeril's Restaurants by Emeril Lagasse.
Emeril Lagasse is a chef, restaurateur, and televsion and radio personality. He is the chef-proprietor of 12 restaurants and the author of 15 cookbooks. He has hosted more than 2,000 shows on the Food Network, serves as the food correspondent for "Good Morning America" and has a radio program called "Cooking with Emeril." Lagasse has received numerous awards, including Best Southeast Regional Chef from the James Beard Foundation. In 2011, he was honored by the James Beard Foundation for his efforts to further the culinary arts in America, as well as his philanthropic work through the Emeril Lagasse Foundation.