Preheat oven to 400°F. Spray 10 x 15 in. jelly roll pan with vegetable pan spray; line with parchment paper and spray again.
In small bowl, sift together flour and cocoa powder.
In large bowl, whisk egg yolks and 1/2 cup sugar with an electric mixer until thick and pale yellow, about 3 minutes. In large bowl, combine egg whites, 1/4 cup sugar and salt. Whisk on high speed with electric mixer until foamy; add cream of tartar and vanilla. Continue whisking until the whites are glossy and form stiff peaks, about 5 minutes. Carefully fold 1/3 beaten egg whites into yolk mixture until just combined. Gently fold in remaining egg whites and flour mixture until there are no streaks visible. Spread into prepared pan.
Bake 10-12 minutes or until toothpick inserted in center comes out clean. Remove cake from oven and immediately turn onto clean kitchen towel; remove parchment paper. Roll cake up in the towel from the long side and let cool 1 minute. Unroll and let cool for 5 minutes. Re-roll in towel and let cool completely.
To assemble, unroll cake and spread with ice cream. Re-roll and freeze until firm, at least 6 hours or overnight. Sprinkle with confectioners? sugar just before serving.