Bring a 4-quart saucepan of well-salted water to a boil. Have a bowl of ice water ready. Boil the peas until just tender, about 4 minutes. Drain, plunge into the ice water to cool, drain again, and set aside.
Cut large radishes or turnips into 1-inch wedges or pieces.
Combine the radishes, broth, butter, and sugar in a 12-inch skillet. Cover and cook over medium heat until almost tender, 4 to 6 minutes. Add the turnips, season lightly with salt and pepper, cover, and reduce the heat to low. Simmer until the turnips and radishes are tender enough to pierce easily with a paring knife, 10 to 12 minutes more.
Stir in the scallions. Cover and simmer until the scallions wilt, 1 to 2 minutes. Add the peas, and pile the spinach on top. Cover and simmer until the spinach wilts, 2 to 3 minutes. Toss to combine. Using a slotted spoon, transfer the vegetables to a warm serving platter, leaving any liquid behind.
Boil the liquid over medium-high heat to reduce it until it just covers the bottom of the skillet, about 1 minute. Stir in the vinegar, and pour the liquid over the vegetables. Season to taste with salt and pepper, toss, and serve.
Make Ahead Tips
You can blanch the snap peas 8 to 12 hours ahead; cover and refrigerate.
nutrition information (per serving):
6, Fat Calories
60, Saturated Fat
4, Monounsaturated Fat
12, Polyunsaturated Fat
Photo: Scott Phillips