Place potatoes and 1 tablespoon of the salt in a large pot with water to cover by 1 inch. Bring to a boil; cook until potatoes pierce easily with a knife, 15 to 20 minutes.

Meanwhile, melt butter in a medium-size heavy saucepan over medium-high. Cook, stirring constantly, until butter browns and is fragrant, about 4 minutes. Remove from heat, and immediately pour into a medium-size heatproof bowl. Set aside at room temperature to cool slightly without stirring. 

Preheat broiler to high with oven rack 8 inches from heat. Drain potatoes well, and return to pot. Add 1/2 cup of the cream, and blend with a hand mixer until potatoes are very smooth. Beat egg yolks, 1 at a time, into potatoes. Slowly pour in browned butter, discarding any browned bits that have settled at the bottom of the pan. Add Parmesan, 1/2 teaspoon pepper, and remaining 1/2 cup cream and 2 1/2 teaspoons salt, and beat until smooth. Transfer to a lightly greased (with cooking spray) 3-quart baking dish.

Broil until top is browned, 5 to 8 minutes. Sprinkle with chives and pepper.