In a medium saucepan, whisk together sugar, cornstarch, and salt until well combined. Stir in cherries and lemon juice until well coated. Bring to a boil over medium-high heat, stirring frequently until sugar dissolves. Reduce heat to medium; cook, stirring frequently, until mixture is thick and has reduced to 3 cups (about 771 grams), 10 to 15 minutes. Remove from heat; stir in liqueur and vanilla. Let cool completely before using.