To prepare meringues, combine first 3 ingredients in a bowl; beat with a mixer at high speed until foamy. Add sugar, 1 tablespoon at a time, beating until stiff peaks form. Fold in pecans. Carefully spoon meringue mixture into a zip-top plastic bag; seal. Trace 1 (10-inch) circle onto each of 2 sheets of parchment paper; tape 1 sheet onto each of 2 baking sheets. Cut 1/4 inch off 1 corner of bag; squeeze meringue mixture onto prepared pans to form 2 (10-inch) circles. Bake meringues at 200° for 3 hours or until dry. Turn oven off; cool in closed oven. Carefully remove meringues.
To prepare mousse, combine water and gelatin; let stand 5 minutes. Place brown sugar, 4 1/2 teaspoons whipping cream, butter, syrup, and salt in a sauce- pan over medium-high heat; bring to a boil, stirring until sugar dissolves. Cook 2 minutes without stirring; remove from heat. Stir in gelatin mixture; cook 30 seconds, stirring until gelatin dissolves. Remove from heat. Transfer mixture to a large bowl; cool completely.
Place remaining 1/4 cup whipping cream in a medium bowl; beat with a mixer at high speed until stiff peaks form. Fold whipped cream into cooled gelatin mixture; chill 20 minutes or until almost set. Combine granulated sugar and 1/4 cup water in a small sauce- pan over medium-high heat; bring to a boil, stirring just until sugar dissolves. Cook without stirring until a thermometer registers 250° (about 3 minutes). Place 2 egg whites and a dash of salt in a large bowl; using clean, dry beaters, beat with a mixer at high speed until foamy. Slowly pour hot sugar mixture in a thin stream into egg whites; continue beating until stiff peaks form. Reduce mixer to medium speed; beat until mixture cools (about 8 minutes).
Fold one-third of egg white mixture into caramel mixture; gently fold in remaining egg white mixture. Chill 1 hour. Place 1 baked meringue round on a platter; spread mousse evenly over meringue. Top with remaining meringue round. Drizzle melted chocolate over top. Cut into 6 wedges.