In a nonstick 5- to 6-quart pan over medium heat, frequently stir 1/2 cup butter, brown sugar, corn syrup, cayenne, and salt until melted and smooth, about 5 minutes.
Add peanuts, cashews, sunflower seed, and sesame seed. Turn heat to high and stir until mixture is very thick and nuts begin to brown, 4 to 6 minutes.
Immediately pour mixture onto buttered foil, spreading as thinly as possible with back of a spoon. Cool until mixture is lukewarm, about 15 minutes.
With your hands, release brittle from foil, then pull or break it into bite-size pieces. When cool, immediately store airtight (otherwise, the coating absorbs moisture and gets sticky).
