Preheat oven to 325ºF. Line a baking sheet with foil. Spread pecans evenly over baking sheet in a single layer. Toast until pecans become fragrant, 5-7 minute Do not let burn. Remove from baking sheet and chop nuts in 1/2. Set aside.
In small container with lid, combine vinegar, oil, mustard, shallots, salt, and pepper. Secure and shake until emulsified and well blended.
Add escarole to large salad bowl. Drizzle dressing to toss. Sprinkle pecans over salad.