In a heavy medium saucepan, combine the whipping cream, Irish cream liqueur, sugar, and vanilla extract.

Bring the mixture to a boil over medium-high heat, stirring frequently to prevent scorching.

In a small bowl, whisk together the cornstarch and water until smooth.

Once the cream mixture is boiling, whisk in the cornstarch slurry.

Continue to boil the sauce, stirring constantly, until it thickens to your desired consistency, about 3 minutes.

Remove the saucepan from the heat and let the sauce cool slightly.

Transfer the sauce to an airtight container, cover, and refrigerate until completely cold, about 2 hours.

The sauce can be made up to 3 days in advance and stored in the refrigerator until ready to serve.