Preheat the oven to 350 degrees F.
Roast the nuts for 10 minutes on a parchment-lined baking sheet. Meanwhile, whisk together the maple syrup, brown sugar, rosemary, butter, and sea salt in a large bowl. Add the warm nuts, tossing to coat.
Dump the nuts back onto the parchment-lined tray and bake for another 10 minutes. Let cool on a cooling rack until crisp and cool.
MAKE AHEAD: Store for up to a week in an airtight container.
*This will make moderately spicy nuts. Feel free to decrease or increase the amount of cayenne according to your taste buds!