How to Make It
In a medium bowl, whisk 1/2 cup of the vinegar with the sugar and 1/2 teaspoon of salt until the sugar dissolves. Add the onion and toss. Let stand at room temperature, tossing occasionally, until the onion is bright pink and crisp-tender, about 30 minutes. Drain well.
In a serving bowl, whisk the buttermilk with the olive oil, pepper, garlic and the remaining 2 tablespoons of vinegar. Season the dressing with salt. Add the escarole, brussels sprouts, almonds and pickled onion and toss. Season with salt and toss again; serve.