Chocolate Truffle Cake
["1 lb. sweet, semi-sweet or bittersweet chocolate, in chunks", "10 Tbsp. sweet butter, softened", "1 Tbsp. sugar", "1 Tbsp. flour", "4 large eggs, separated", "pinch of salt"]
["Preheat oven to 425\u00b0.", "Butter sides and bottom of 8-inch spring-form pan.", "Line the bottom with a round of waxed paper, cut to fit.", "Butter the paper and dust it lightly with flour."]
["sweet", "sweet butter", "sugar", "flour", "eggs", "salt"]