Preparation

• Set a heavy 9- to 10-inch skillet over high heat with the olive oil and butter. When the butter has melted, stir in the leeks, turnips, and carrots, and cook for 1 minute, stirring once or twice. Season with salt, cover, reduce the heat to medium low, and cook for 5 minutes. Uncover and cook at a medium sizzle, stirring occasionally, until the carrots and turnips are almost completely tender and are nicely — but lightly — browned, about 25 minutes. (After about 15 minutes, the vegetables should be just starting to brown, so lower the heat if they’re cooking too quickly.)
• Reduce the heat to very low and continue cooking until tender, about 5 minutes more. Turn off the heat, season to taste with pepper and more salt, if necessary. Gently fold in the tarragon or basil. Transfer to a warm serving dish, sprinkle with the parsley (or fold it in as well), and serve.