In a medium bowl, whisk the yolks and 1/4 cup brown sugar until combined.
In a medium sized, heavy bottomed saucepan, stir together cream milk, salt, and remaining 1/4 cup brown sugar. Bring to a simmer over medium-high heat, then reduce the heat to medium.
Carefully and slowly add a ladle-full of the hot cream mixture to the egg mixture, whisking the eggs constantly. Repeat with two more ladles of cream, adding slowly and whisking constantly. Using a heatproof rubber spatula, stir the cream mixture in the saucepan as you slowly add the egg mixture to the pan.
Cook the mixture over medium heat, stirring constantly, until it is thick, coats the back of a spatula, and holds a clear path when you run your finger across the spatula, about 2 minutes.
Pour the mixture through a fine mesh strainer into a clean container. Set the container in an ice-water bath, and use a clean spatula to stir the base occasionally until cooled. Remove the container from the ice water bath, cover tightly, and refrigerate for two hours or overnight.
Once the base is chilled, freeze in an ice cream machine according to manufacturer’s instructions.
While the ice cream is churning, make the mix-in. In a small bowl, combine honey and grape nuts. Once the ice cream is done in the ice cream machine, carefully fold in large chunks of the cereal mixture. Transfer the ice cream to a covered container and freeze for a minimum of two hours.
Homemade ice cream will stay good for about 1 week but is best enjoyed within a few days.