Heat oven to 375 degrees. Bring a pot of water to a boil. Add haricots verts and 1 tablespoon salt; cook until just tender, 3 to 4 minutes. Drain, and plunge into an ice-water bath to chill. Drain, and set aside. (This can be done up to a day in advance.)
In a medium skillet, melt 1 1/2 tablespoons butter over medium-high heat. Add shallots, 1/2 teaspoon salt, and 1/8 teaspoon pepper, and cook, turning, until shallots start to brown on all sides, 2 to 3 minutes. Cover, reduce heat to low, and cook, turning frequently, until shallots are well browned, about 15 minutes. Let cool slightly, then cut into slivers.
Meanwhile, place hazelnuts (blanched or with skin) in a baking pan; toast in the oven until they darken, 5 to 7 minutes. If using hazelnuts with skin, remove as much of it as possible by rubbing them quickly and vigorously in a dish towel. Crush roughly with the flat side of a knife.
In a large skillet, heat remaining 2 tablespoons butter over medium-high heat. Add haricots verts, remaining 1/2 teaspoon salt, and remaining 1/8 teaspoon pepper; cook, stirring, until heated through, about 3 minutes. Add shallots and hazelnuts; cook 1 minute more. Transfer to a serving dish, and serve.