In a heavy saucepan, heat half-and-half to 175°; stir in the brown sugar until dissolved. Whisk a small amount of hot cream mixture into the eggs; return all to the pan, whisking constantly. Cook and stir over low heat until mixture reaches at least 160° and coats the back of a metal spoon. Do not allow to boil. Remove from heat immediately.
Quickly transfer to a small bowl; place bowl in a pan of ice water. Stir gently and occasionally for 2 minutes. Stir in whipping cream and vanilla. Press plastic wrap onto the surface of custard. Refrigerate for several hours or overnight. Stir in your flavorings.
Fill cylinder of ice cream maker no more than two-thirds full; freeze according to manufacturer’s directions. Transfer ice cream to freezer containers, allowing headspace for expansion. Freeze until firm, 2-4 hours. If desired, serve with toppings.