Preheat the grill. Lightly steam the endive, then coat with olive oil and sprinkle with sea salt and fresh pepper. Grill; cut side down, and sear, turning once, until golden brown but still firm in the middle. Transfer to heated serving platter.

To prepare the sauce, simmer the vinegar in a small saucepan for about one minute. Remove from heat and whisk in the butter, a small amount at a time, until smooth. Whisk in the chopped fresh rosemary. Season with sea salt and fresh pepper.

Drizzle the Balsamic butter over the endive and serve. Makes six servings.