Make the Ice Cream Custard: In a medium saucepan over medium-low heat, warm the milk and sugar, stirring occasionally, until the sugar has dissolved. Meanwhile, pour the heavy cream into a large bowl and set a mesh strainer on top.
In a medium bowl, whisk together the egg yolks. Slowly pour the warm milk mixture into the egg yolks, whisking constantly. Then, pour the mixture back into the saucepan.
Stir the mixture constantly over medium heat with a heatproof spatula, making sure to scrape the sides and bottom of the pan occasionally. Keep stirring until the mixture thickens and coats the back of the spatula (if you're using an instant-read digital thermometer, the mixture should be between 170 and 175 degrees F). Pour the custard through the mesh strainer and stir it into the cream. Add the maple syrup, vanilla extract and salt; stir to combine. Allow the mixture to cool to room temperature, stirring occasionally (you can speed up the process by placing the bowl in an ice bath), then cover and refrigerate for at least 8 hours, or overnight.
Make the Maple-Glazed Walnuts: Heat the maple syrup in a small skillet or saucepan over medium-high heat until it just begins to come to a full boil. Add the walnuts, stir to coat them, then allow the mixture to cook until it again comes to a full boil. Once it reaches a full boil, stir for 10 seconds, then remove the pan from the heat and allow to cool completely (the walnuts will still feel wet and sticky when cool).
Churn the Ice Cream: Freeze the custard mixture in an ice cream maker according to the manufacturer's directions. Add the maple-glazed walnuts during the last few minutes of churning. Transfer to a freezer-safe container and store in the freezer.