Preheat an oven to 300ºF. Line a large baking sheet with parchment paper or silicon baking sheet. In a food processor fitted with the metal blade or blender, combine the chocolate and brown sugar and process until the chocolate is very fine. Sift together the flour, cocoa, chai powder, baking soda and salt into the chocolate-sugar. In the bowl of a mixer, combine the eggs, vanilla extract and chai concentrate. Using the paddle attachment Set mixer to med-low and beat. Reduce the speed to low and add in the sugar and flour mixtures until a stiff dough forms. On a floured surface, divide the dough in half. Form each half into a loaf 12 inches long. Place loaves on lines baking sheet being sure they have enough space between them not to touch once risen. Bake until they hold their shape even when touched. (aprox 45 minutes ) Remove from the oven and let cool slightly. (Do not turn off oven) Carefully transfer the logs to nonstick cutting board. Using a pastry cutter or serrated knife, cut loaves on the diagonal into slices 3/4 inch thick. Place the slices, cut side down, on the baking sheet. Bake for 25 minutes. Turn the slices over and bake until crisp and dry, about 25 minutes more. Remove and allow to cool on baking sheet.