In a food processor, pulse together walnuts and 4 tablespoons cocoa powder until they form the consistency of crumbled chocolate cookies. Add remaining ingredients and pulse until mixture is sticky and holds together; this should only take 10-15 seconds.Turn dough out onto a baking sheet and roll into whatever size balls you like. Mine are approximately 1 1/2" in diameter. Sprinkle with extra sea salt, if using. Freeze, gently covered with plastic wrap, for 20 minutes OR refrigerate for 1 hour before enjoying. Keep leftovers tightly sealed in the refrigerator up to 1 week.