How to Make It
Preheat the oven to 400°. Spread the walnuts on a baking sheet and toast for about 6 minutes, until fragrant and lightly browned.
In a large pot of boiling salted water, cook the brussels sprouts until bright green and almost tender, about 6 minutes; drain. Immediately plunge the brussels sprouts into ice water to stop the cooking. Pat dry with paper towels.
In each of 2 large skillets, cook half of the butter over high heat until it begins to brown. Add the brussels sprouts in an even layer and cook without stirring until they brown on the bottom, about 8 minutes. Add the vinegar and cook, stirring, until the vinegar reduces and glazes the brussels sprouts, about 3 minutes. Season with salt and pepper, stir in the walnuts and mint and serve at once.