Wash and pit 1.5 pounds of fresh, ripe plums, then slice them into quarters. Arrange the plums into a medium saucepan and add ¼ cup of water. Cover and cook over medium heat for 10-15 minutes until soft.

Remove from heat and cool slightly. Blend the plums in a blender until smooth, yielding about 2 cups of puree.

Combine ½ cup of the puree with the granulated sugar or light corn syrup in the saucepan. Heat gently over low heat and stir until the sugar dissolves, about 3-5 minutes.

Stir the sweetened mixture back into the remaining puree. Mix in 2 tablespoons of your chosen liqueur and 1 tablespoon of fresh lemon juice until well combined.

Cover and refrigerate the mixture for at least 8 hours or overnight to chill thoroughly.

Pour the chilled mixture into your ice cream machine and churn according to manufacturer's instructions for 20-30 minutes until creamy.

Transfer to an airtight container, smooth the top, and freeze for at least 4 hours to firm up.

Before serving, let the sorbet sit at room temperature for 5-10 minutes to soften slightly for easier scooping. Optionally garnish with fresh mint leaves.