Whisk together first 4 ingredients in a 3-quart saucepan. Stir together half-and-half and instant coffee. Gradually whisk into the saucepan. Cook over medium heat, whisking constantly, until mixture comes to a boil. Cook 1 minute or until mixture is thickened and bubbly. Remove from heat; whisk in butter and vanilla. Cover and chill 4 hours.