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.
Andrea Reusing is the creator of the restaurant Lantern in Chapel Hill, N.C., and author of the book Cooking in the Moment: A Year of Seasonal Recipes. In this installment of The Key 3, she shares with Lynne Rossetto Kasper the techniques behind three of her favorite recipes: Turnip Soup, Overnight Braised Short Ribs and Tomato Salad.