Preheat the oven to 375°F.
Remove the leaves (needles) from the rosemary and chop fine.
Roast the cashews on a baking sheet for 10 to 15 minutes until roasted. Keep an eye on the cashews so they don't burn.
When toasted a golden brown, remove from oven and combine with the rosemary, salt, olive oil, black pepper and red pepper flakes.
Taste and adjust the seasonings. If you like them hotter, add a little more red pepper flakes. Saltier? More salt.