Heat a large straight-sided skillet over medium heat until hot. Add the oil, shallots, garlic and pepper flakes, if using, then season with 1/4 teaspoon salt. Stir with a wooden spoon until the shallots are soft and fragrant, about 3 minutes. Add the olives and raisins and stir to combine. Add the chopped escarole and season with the remaining 3/4 teaspoon salt. Stir to combine and coat the escarole in the flavors. Cover with the lid and allow to steam for 5 minutes. Remove the lid and increase the heat to medium-high. Cook, stirring often, until the liquid has evaporated and the greens are tender, another 3 minutes.