Preheat oven to 250°F. In large frying pan, combine sugar and water over medium-high heat and cook until sugar dissolves and syrup comes to a boil. Add the walnuts, butter, a pinch or two of salt, and cook, stirring constantly, until syrup coats the nuts and almost no liquid syrup is left in the pan.

Line a sheet pan with a Silpat or parchment. Spread the nuts out on the prepared baking sheet and oven-toast for 15–20 minutes, they will crisp more as they cool but be careful tasting or you will burn your mouth! Allow to cool at least 10 minutes before tasting.