In a small pot, simmer cream, milk, sugar, 1/4 cup maple syrup and salt, about 5 minutes. Remove pot from heat.
In a separate bowl, whisk yolks and vanilla extract. Whisking constantly, slowly whisk 1/3 of the hot cream into the yolks, then, whisk the yolk mixture back into the pot with the cream. Return pot to medium-low heat and cook until mixture is thick enough to coat the back of a spoon.
Cool mixture at room temperature. Cover with plastic wrap and chill for at least 4 hours or overnight.
Churn cooled base in an ice cream machine according to manufacturer's directions.
Scoop finished ice cream into a freezer-safe bowl and garnish with chopped walnuts and drizzle 2 tablespoons maple syrup.
Serve Black Walnut Ice Cream directly from the bowl as soft serve, or store in the freezer until ready to eat.
Make a delicious Black Walnut Ice Cream Sundae by serving scoops with Banana Walnut Muffins and caramel sauce.