In a small saucepan, combine sugar and cornstarch; stir in water until smooth. Add cherries. Bring to a boil over medium heat; cook and stir for 2 minutes or until thickened. Remove from the heat; stir in extract. Refrigerate until chilled.
In another saucepan, combine the sugar and cornstarch; stir in milk until smooth. Bring to a boil over medium heat. Reduce heat; cook and stir for 2 minutes. Remove from heat. Whisk a small amount of hot mixture into egg yolks; return all to the pan, whisking constantly. Bring to a gentle boil; cook and stir for 2 minutes.
Remove from the heat. Stir in chocolate and vanilla until chocolate is melted. Cool to room temperature. Fold in whipped cream
Spoon 1/4 cup mousse into each parfait glass. Top with a rounded 1/4 cup of cherry mixture. Repeat layers. Refrigerate until chilled. Yield: 6 servings.