PLace pumpkin seeds in a small dry skillet over medium heat. Toast, shaking the pan often until the seeds begin to pop, 2-3 minutes, remove from the skillet and set aside.
Grease a baking sheet or line with silicon baking mat. Have ready a white plate and wooden skewer to test the doneness of the caramel.
In a medium pan, combine sugar, water and tartar. Stir until the sugar dissolves. Cover and simmer without stirring for 2-3 minutes, uncover and wash down the insides of the pan using a pastry brush. Continue simmer until the syrup begins to color. You want it to be medium dark amber. Use the white plate and skewer to test.
Once the syrup is the desired color/ doneness, quickly stir in the seeds, nibs and cayenne. Working quickly, pour the mixture onto the prepared pan and spread as thinly as possible.
Allow to cool completely before breaking into smaller pieces for storage. Store in a single layer in a tightly covered container.