1. In a large skillet, combine the sugar and butter. Set over medium heat and stir until the sugar is dissolved. Stir in the jelly and lemon juice. Simmer for 2 minutes to reduce slightly. Stir in the cherries and bring to a boil. Add the Cognac and heat 30 seconds longer. Standing away from the pan and using a long match, carefully ignite the cherries.
2. When flames die down, spoon the cherries and sauce over scoops of ice cream in individual dessert bowls. Serve immediately.