- Shell the beans. Bring a saucepan three-fourths full of water to a boil over medium-high heat. Add the beans and cook until very soft, about 20 minutes. Drain, reserving 1 cup of the liquid.
- Prepare a fire in a grill or preheat a broiler. In a fry pan over medium heat, combine the beans, garlic, sage and 2 tablespoons of the oil. Cook, mashing the beans with a spoon or potato masher and adding the reserved cooking liquid as needed to keep the mixture moist, until a rough paste forms, 10 to 15 minutes. Remove from the heat and continue mashing the beans to form a smooth paste. Alternatively, pulse the mixture in a food processor fitted with the metal blade or in a blender. Season with salt and pepper.
- Lightly brush the bread slices on both sides with olive oil and place on the grill rack or on a baking sheet. Grill or broil, turning once, until golden on both sides, 30 to 60 seconds on each side. Remove from the heat and set aside.
- In another fry pan over high heat, warm the remaining 1 tablespoon oil. Add the escarole and cook, tossing frequently with tongs, until wilted, 2 to 3 minutes. Add the vinegar and red pepper flakes and season with salt and pepper. Mix well.
- To serve, spread the bean puree on the grilled or toasted bread, dividing it evenly. Top with the wilted escarole and serve immediately.