How to Make It
In a small saucepan, cover the prunes with the tea and bring to a simmer. Remove from the heat, cover and let stand until the prunes are plump, about 1 hour. Drain the prunes and discard the tea.
Melt 4 tablespoons of the butter in a skillet. Add the carrots and turnips and season with salt and pepper. Cook over moderate heat, stirring, just until heated through, 2 minutes. Add enough water to cover the vegetables by 1 inch and bring to a boil. Simmer over moderate heat until tender, 7 minutes. Drain the vegetables.
In a medium saucepan, cover the radishes with the chicken stock and soy sauce and bring to a boil. Simmer over moderate heat until the radishes are tender, 10 minutes. Drain, reserving the cooking liquid.
In a large enameled cast-iron casserole, melt the remaining 2 tablespoons of butter. Add the potatoes and cook over moderate heat, stirring, until tender and golden, about 8 minutes. Add the onion and cook until softened, about 4 minutes. Stir in the garlic and cook until fragrant, 1 minute. Add the prunes, carrots, turnips and the radishes with their cooking liquid and season with salt and pepper. Add the thyme and bring to a simmer. Cook over moderately low heat, stirring, until the vegetables are tender and the liquid is slightly reduced, about 8 minutes. Discard the thyme sprig. Serve with lemon wedges.