Preheat oven to 400 degrees F (200 C). Butter an 18 x 13-inch jelly-roll pan and line with parchment paper. Butter and flour paper, tap out excess flour.
Using electric stand mixer and whisk attachment, beat brown sugar, eggs, sugar and salt in large bowl until very thick ribbon falls when attachment is lifted, about 8 minutes. Sift cocoa powder and flour over egg mixture, then fold in using rubber spatula.
Pour batter into prepared pan, spreading evenly with off-set spatula. Bake until cake is springy to the touch, about 10 minutes. Transfer pan to cooling rack and cool completely.
Combine 1/4 cup cream and white chocolate in large wide metal bowl. Scrape in seeds from vanilla bean. Stir over saucepan of simmering water until chocolate melts and mixture is smooth. Place hot water in small bowl. Sprinkle gelatin over. Heat gelatin mixture in microwave in 10 second intervals until gelatin dissolves, about 20 seconds total. Stir gelatin mixture into warm white chocolate mixture. Cool to room temperature, stirring occasionally.
Using electric mixer, beat remaining 1 1/4 cups cream in large bowl just until stiff peaks form. Fold into cooled white chocolate mixture.
Using off-set spatula, spread filling evenly over cake. Refrigerate until filling begins to set. Beginning with one short side and peeling parchment paper from cake while rolling, roll up cake jelly-roll style. Discard parchment paper. Transfer cake to platter, seam side down. Cover and chill until filling is set, about 2 hours.
Roulade may be made 1 day ahead. Keep refrigerated.
Lightly dust roulade with confectioners' sugar. Cut crosswise and serve.
Makes 10 servings.
Date: June 17, 2004