You may have seen little squares of Tcho chocolate in their brightly colored wrappers decorated with futuristic parabolas of gold and silver. They’re easily found: Starbucks has sold them; Whole Foods sells them now. Those usually aren’t the stores you visit to track down handcrafted chocolate from bean-to-bar makers, the new wave of chocolate producers that find and blend the rarest and most richly flavored cacao beans. Artisans like Mast Brothers, in Brooklyn, promise that each batch of bars will be different; nothing will be blandly mass-produced. In a video on their website, the lavishly bearded Mast siblings extol the “inconsistency” of their chocolate. Inconsistency generally isn’t what gets you orders from Starbucks and Whole Foods.