Preparation Preheat oven to 375°F. Spray round 6 1/2-inch-diameter disposable aluminum pan or 9 1/4x6 1/2x1-inch rectangular disposable aluminum pan with nonstick spray. Stir chocolate and butter in medium metal bowl over saucepan of simmering water until melted and smooth. Stir in orange peel. Remove bowl from over water. Using electric mixer, beat eggs and salt in large bowl until tripled in volume, about 5 minutes. Fold 1/4 of egg mixture into lukewarm chocolate mixture to lighten. Gently fold chocolate mixture into remaining egg mixture just until blended (do not overblend or mixture will deflate). Transfer batter to prepared pan. Bake until sides are set and center is soft, about 25 minutes for round cake or 12 minutes for rectangular cake. Transfer pan to rack and cool 30 minutes. Using scissors, cut several slits in sides of round pan or corners of rectangular pan. Fold down pan sides. Using large metal spatula, transfer cake from pan to platter. Sprinkle with powdered sugar. Serve warm.
Preparation Preheat oven to 375°F. Spray round 6 1/2-inch-diameter disposable aluminum pan or 9 1/4x6 1/2x1-inch rectangular disposable aluminum pan with nonstick spray. Stir chocolate and butter in medium metal bowl over saucepan of simmering water until melted and smooth. Stir in orange peel. Remove bowl from over water. Using electric mixer, beat eggs and salt in large bowl until tripled in volume, about 5 minutes. Fold 1/4 of egg mixture into lukewarm chocolate mixture to lighten. Gently fold chocolate mixture into remaining egg mixture just until blended (do not overblend or mixture will deflate). Transfer batter to prepared pan. Bake until sides are set and center is soft, about 25 minutes for round cake or 12 minutes for rectangular cake. Transfer pan to rack and cool 30 minutes. Using scissors, cut several slits in sides of round pan or corners of rectangular pan. Fold down pan sides. Using large metal spatula, transfer cake from pan to platter. Sprinkle with powdered sugar. Serve warm.