How to Make It
In a medium saucepan, combine 1 cup of the apple cider vinegar with the sugar, 1 tablespoon of kosher salt and 1/4 cup of water and bring to a boil. Add the diced squash and let cool to room temperature. Drain the squash.
Meanwhile, in a food processor, combine the egg yolk with the cheese, sage, garlic, lemon juice and the remaining 2 tablespoons of vinegar. With the machine on, drizzle in the oil until the dressing is emulsified. Season with salt and pepper.
In a large bowl, toss the escarole with the sage dressing and season with salt. Arrange the greens on plates, top with the pickled squash and serve.