In a heavy, medium nonaluminum saucepan, whisk together the egg yolks and the brown sugar until thick.
In another medium saucepan, bring the cream and half-and-half just to a boil over moderate heat. Gradually whisk the hot cream into the egg yolk mixture in a thin stream.
Cook over low heat, stirring constantly, until the custard is thick enough to coat the back of a spoon, about 6 minutes; do not boil.
Immediately strain the custard into a medium bowl. (DON’T skip this step—because you mixed the yolks with the brown sugar, inevitably some of the yolks won’t blend, and will turn instead into little teeny flecks of scrambled eggs. You need to strain those out)
Stir in the vanilla and let cool to room temperature, stirring occasionally, about 30 minutes. Cover and refrigerate until very cold, at least 5 hours. Pour the cold custard into an ice cream maker and freeze according to the manufacturer’s instructions. Let the ice cream soften slightly before serving.
**Note: I used 1 cup heavy cream and 3 cups whole milk to good effect. I think as long as you maintain the four cups of dairy you will be fine.