Step 1Heat the oven to 375 degrees. Line 2 large, rimmed baking sheets with parchment paper.
Step 2Combine the pumpkin seeds and the half egg white in a very large stainless steel bowl and toss to coat. Sprinkle the sugar, salt, paprika and 1/4 to 1/2 teaspoon cayenne over the seeds and toss until well and evenly coated. Divide the seeds between the 2 prepared sheets and spread out in an even layer.
Step 3Bake the seeds 5 minutes. Remove the sheets from the oven and shake or stir the seeds to keep them from sticking or burning. Return them to the oven for 5 minutes, then stir or shake again. Repeat one or two more times, until the seeds are crunchy but not browned. They'll get crunchier after they've cooled. (They may clump a bit -- you can leave them that way or let them cool and then break them apart.) Remove from the oven and cool on racks. Serve warm or store indefinitely in airtight containers.