Use your blender or food processor to prepare enough peach puree for both the ice cream and the Chocolate-Peach Sauce. Should you have leftover peach ice cream, drops scoops into glasses of cold lemon-lime soda for a fantastic float.
Cut peaches into chunks and place in a food processor or blender. Cover and process or blend until smooth. Measure 2 cups of the peach puree for the ice cream; cover and chill. Measure and set aside 2 tablespoons of the peach puree for the Chocolate-Peach Sauce (if using). Cover and chill any remaining puree for another use.
In a large saucepan combine half-and-half and sugar. Cook and stir over medium heat until sugar is dissolved. Gradually stir about half of the hot mixture into the egg yolks. Add yolk mixture to cream mixture in saucepan. Cook and stir about 5 minutes more or until mixture is slightly thickened and coats the back of a metal spoon. Remove from heat. Transfer to a large bowl; cover and cool for 30 minutes. Stir in vanilla.
Cover and chill for 4 to 24 hours. Stir in the 2 cups chilled peach puree. Freeze mixture in a 4- or 5-quart ice cream freezer according to the manufacturer's directions. Ripen at least 4 hours. If desired, serve ice cream with Chocolate-Peach Sauce.
In a small saucepan bring half-and-half just to boiling. Turn off heat and stir in semisweet chocolate. Stir until the chocolate is melted. Stir in reserved peach puree and peach liqueur. Let cook slightly. Makes about 1-1/2 cups sauce.