
Line a baking sheet or large plate with parchment paper. Set aside.
Place the walnuts, butter, and maple syrup into a large skillet pan set over high heat. Bring the butter and maple syrup to a boil.
Reduce the heat to low and stir, making sure all of the walnuts are coated in maple syrup and butter. Let the walnuts simmer over low heat for 2 minutes.
Remove the pan from the heat and pour the walnuts onto the parchment paper. Spread them out so they are not touching. Sprinkle with sea salt.
Place the walnuts in the refrigerator until they are cool, about 5 minutes.