Preheat oven: Heat oven to 325°F (165°C). Line a rimmed baking sheet with parchment paper.
Mix the coating: In a large bowl, whisk together melted butter, olive oil, rosemary, thyme, salt, pepper, garlic powder, and cayenne (if using).
Toss the nuts: Add the mixed nuts to the bowl and toss until evenly coated.
Spread on baking sheet: Arrange nuts in a single layer on the prepared baking sheet.
Bake: Roast for 20-25 minutes, stirring halfway through, until golden and fragrant.
Cool completely: Let the nuts cool on the baking sheet — they'll crisp up as they cool.
Serve or store: Transfer to a serving bowl, or store in an airtight container for up to one week.