Preheat oven to 325F. Spray 15-1/2 x 10-1/2-inch jelly-roll pan with nonstick cooking spray; line pan with waxed paper; spray paper with cooking spray. In small bowl with mixer at high speed, beat egg whites until soft peaks form. Gradually add 2 tablespoons sugar, continuing to beat until stiff but not dry. In large bowl, beat egg yolks, 1 teaspoon Sweet'N Low and remaining 2 tablespoons sugar until thick and lemon colored. Beat in water and vanilla.
In small bowl, stir together cake flour, 3 tablespoons cocoa, baking powder and salt; beat into egg-yolk mixture. Gently fold egg whites into egg-yolk mixture. Spread batter in pan. Bake 12 to 15 minutes or until cake springs back when touched in center. Immediately invert cake onto paper towel sprinkled with 1 tablespoon cocoa. Peel waxed paper from cake. Starting at narrow end, roll cake with towel, jelly-roll fashion. Place cake, seam-side down, on wire rack to cool completely.
Meanwhile, prepare filling: In cup, mix hot water with instant espresso coffee until completely dissolved. In large bowl with mixer at medium speed, beat ricotta cheese, yogurt, 1 tablespoon cocoa, 3/4 teaspoon Sweet'N Low, granulated sugar and coffee mixture until smooth. Cover and refrigerate until ready to use.
Unroll cake. Spread with filling, reserving 1/4 cup for garnish. Roll cake without towel. Using small strainer, sprinkle cake with confectioner's sugar. Pipe on remaining filling. Serve immediately or refrigerate.