How to Make It
Preheat the oven to 350°. Spread the walnuts, pecans and hazelnuts on a rimmed baking sheet and bake for 10 minutes, until toasted. Let cool, then coarsely chop.
In a medium saucepan, combine the 3 syrups with the sugar, vanilla bean seeds and 1/2 cup of water. Bring to a boil over high heat, then reduce the heat to moderate and simmer until thickened, 8 minutes. Remove from the heat and stir in the chopped nuts. Let cool completely, then transfer to a container and refrigerate. Serve at room temperature.