2 cups whipping cream
6 tablespoons Irish cream liqueur
1/4 cup sugar
1/2 teaspoon vanilla extract
2 teaspoons cornstarch
2 teaspoons water
Bring cream, liqueur, sugar, and vanilla to boil in heavy medium saucepan over medium-high heat, stirring frequently. Mix cornstarch and 2 teaspoons water in small bowl to blend; whisk into cream mixture. Boil until sauce thickens, stirring constantly, about 3 minutes. Cool, then cover and refrigerate until cold, about 2 hours.
(Can be made 3 days ahead. Keep refrigerated.)