1 sheet frozen puff pastry, thawed
2 carrots, peeled and cut into 1-inch chunks
1 large yellow onion, chopped
1 sweet potato, peeled and cut into 1-inch chunks
2 parsnips, peeled and cut into 1-inch chunks
4 fresh thyme sprigs, plus 1 Tbs. leaves
1/4 cup olive oil
Salt and freshly ground pepper, to taste
4 Tbs. (1/2 stick) unsalted butter
1/4 cup all-purpose flour
1/2 cup dry white wine
2 1/2 cups vegetable broth