Pour maple syrup into medium sized frying pan and place over medium heat. Once syrup has warmed a bit, add the walnuts and salt. Using a heat-safe spatula, stir to coat all the walnuts. Continue cooking for 3 to 4 minutes, stirring constantly, until walnuts start to smell toasty and syrup has thickened and darkened slightly in color. Pour walnuts out of pan to heat-safe surface and allow to cool completely, about 30 minutes. Break apart as needed.
Notes
Be sure to stir walnuts and maple syrup constantly and remove from heat immediately when done to prevent burning.