1 1/2 cups walnut halves
3/4 cup maple syrup
1 3/4 cups heavy cream
1 1/4 cups whole milk
5 large egg yolks, beaten
1/4 tsp salt

Put the walnuts in a dry skillet over medium heat and toast them while stirring almost constantly,
for about 5 minutes, or until they are fragrant and turning golden.
Watch them carefully because once the oils in the nuts heat up they can burn very fast.
Set aside to cool, and then chop.
Put the maple syrup in a large saucepan and bring to a boil.
Let simmer until reduced to 1/2 cup, about 8-10 minutes.
The syrup will boil up initially, so stay by the pan.
Add the cream, milk, and salt to the pan, and stir.
Drizzle a cup of the warm cream mixture into the egg yolks, while whisking constantly.
Add another cup, and then return it all to the saucepan and continue to cook over medium heat, stirring almost constantly, until the mixture thickens.
Do not let it boil.
Strain through a fine mesh strainer into a bowl and cover with plastic.
Refrigerate until completely chilled, or over overnight.
Process the chilled mixture according to your ice cream machine's instructions.
Add the walnuts in during the last few minutes of processing.
Spread the soft ice cream in a loaf pan or container, cover tightly, and put in the freezer until firm, 6-8 hours, or overnight.

Notes:

DO NOT skip toasting the walnuts, it makes all the difference.
It should go without saying, but use pure maple syrup, not an imitation syrup.