In a large sauce pan, heat milk over medium heat until lightly bubbling.
In a large bowl, beat egg yolks, maple syrup and heavy cream until well blended.
Once milk has reached a simmer, temper egg yolk and cream mixture, by adding hot milk, a ladle full at a time, whisking constantly. Once half of the milk has been added to the egg and cream mixture, whisk it back into the sauce pan with the milk.
Heat over medium heat, whisking constantly until custard thickens slightly and coats the back of a spoon.
Prepare an ice bath and pour custard through a sieve into a bowl over an ice bath, whisk in vanilla. Cool custard completely before adding to ice cream machine.
Chop and lightly toast walnuts. Add chopped walnuts to ice cream mixture towards the end of the churning cycle. Ice cream will be ready to eat with a soft serve texture. Or pack ice cream in an airtight container and freeze overnight for firmer ice cream.