In a medium-sized saucepan, heat the olive oil over medium heat for about 1 minute. Add the cashews and stir to coat.
Cook for 5 to 10 minutes, stirring periodically with a spatula (and more frequently when you start to notice a change in color), until the cashews are golden brown and fragrant. The amount of time will vary by stove.
Line a plate or cutting board with paper towels. Using a slotted spoon, transfer the nuts to the plate to drain; do not pat them dry (the oil will help the seasonings adhere).
While the cashews are still hot, carefully transfer them to a medium-sized bowl and toss with the salt, pepper and rosemary. Serve hot, warm or at room temperature. (I recommend enjoying them hot!)
Notes
You can add more or less rosemary to taste, or omit it completely.