How to Make It
In a small skillet, cook 4 tablespoons of the butter over moderate heat, swirling, until browned, 3 to 5 minutes; let cool completely.
In a bowl, blend the cooled brown butter with the remaining 4 tablespoons of butter and the heavy cream, lemon juice and rosemary. Season with salt.
Light a grill or preheat a grill pan. In a large bowl, toss the radishes with 2 tablespoons of the rosemary brown butter and season with salt. Grill on a perforated grill pan (if using a grill) over high heat, tossing occasionally, until lightly charred and crisp-tender, about 5 minutes. Return the radishes to the bowl. Add the 2 cups of radish greens and the mint; toss well. Pile the radishes and greens on a platter and serve with grilled bread, sea salt and the remaining brown butter.