2 winter squash seeded and cut into 3/4-inch pieces
6 baby waxy potatoes, such as new or blue, cut into 3/4-inch pieces
1 sweet potato, cut into 3/4-inch pieces
3 tablespoons olive oil
Kosher salt and freshly ground black pepper
1 small onion, chopped
1 or 2 leeks
2 garlic cloves, finely chopped
One 15-ounce can tomatoes
Preheat the oven to 425 degrees F.
Toss the squash and potatoes with 2 tablespoons of the oil, salt and pepper. Spread in a single layer on a large rimmed baking pan and roast, stirring once or twice, until tender and golden brown in spots, 15 to 20 minutes.
Meanwhile, heat the remaining tablespoon oil in a medium pot over medium-high heat. Add the onion, garlic, rosemary and a pinch of salt and cook, stirring, until softened, about 8 minutes. Add the tomatoes and roasted vegetables and simmer until slightly thickened and the flavors have blended, about 10 minutes. Transfer to a serving bowl.