Winter-Vegetable Shepherd's Pie
- Put the potatoes in a medium saucepan of salted water. Bring to a boil, reduce the heat, and simmer until the potatoes are tender, about 15 minutes. Drain the potatoes and put them back into the saucepan along with 1 teaspoon of the salt and 1/4 teaspoon of the pepper. Mash the potatoes over very low heat, gradually incorporating the cream and 4 tablespoons of the butter. Cover and set aside.
- Meanwhile, in a Dutch oven, melt the remaining 2 tablespoons of butter over moderately low heat. Add the onions and cook, stirring occasionally, until golden, about 10 minutes. Add the garlic and cook, stirring, until fragrant, about 1 minute. Stir in the sliced mixed vegetables, carrots, thyme, and the remaining 1/2 teaspoon each of salt and pepper. Mix well.
- Stir in the broth and bring to a simmer. Cook over moderate heat, covered, until the vegetables start to soften, 5 to 10 minutes. Uncover, increase the heat to moderately high, and cook until the vegetables are tender and almost no liquid remains in the pan, about 10 minutes longer.
- Heat the broiler. Transfer the vegetables to a 9-inch pie plate, spread the potatoes over the top, and cook until lightly browned, about 5 minutes.