Preheat the oven to 325 degrees F. Spread the plain almonds in a single layer on a baking sheet lined with parchment paper and bake until lightly toasted, 8-10 minutes. Remove from the oven but keep the oven on.
Transfer the hot almonds to a bowl and drizzle the tamari sauce overtop. Stir to evenly coat.
Spread the almonds in an even layer on the same parchment-lined baking sheet. Bake for 5 minutes, and then stir the almonds. Return to the oven for a couple minutes more (2-5 depending on the oven) or until the almonds are dry. (A little bit of moisture is fine; this will dry as the almonds cool.) Watch the nuts carefully after the first 5 minutes so they do not burn.
Remove from the oven and allow to cool completely. The nuts will firm up as they cool. For an optional spicy kick, you may sprinkle the almonds lightly with cayenne pepper while they are still warm.