Prep: Preheat oven to 350°F and line an 8x8" baking pan with parchment. (If you use a 9x9" pan the brownies will be thinner and may be done a few minutes earlier.)
Melt chocolate and butter: If using a chocolate bar, give it a coarse chop to help it melt evenly. Add the dark chocolate to a microwave-safe bowl along with vegan butter and soy milk. Microwave in 30-second intervals, stirring in between, until the mixture is completely smooth and melted. (Alternatively, you can melt over a double boiler.)
Mix dry ingredients: In a separate large mixing bowl, combine all-purpose flour, baking powder, salt, granulated sugar, brown sugar, and cocoa powder. Whisk ingredients together until there are no lumps. (If the cocoa is very lumpy, sift it into the mixture.)
Form the batter: Create a well in the dry ingredients and pour in the melted chocolate mixture. Add the vanilla extract and (optional) instant coffee and stir everything together until about 80% combined. Add in the chocolate chips and use a spatula to fold them in till there are no more dry streaks of flour in the batter.
Bake: Pour batter into prepared baking pan and spread evenly with your spatula. Bake in preheated oven for 35-38 minutes, or until the edges pull away from the sides of the pan and the top is shiny and set. (If you used a 9x9" pan, begin checking for doneness about 10 minutes sooner.)
Cool and slice: The brownies will be quite soft when you first take them out of the oven, so I highly recommend letting them cool in the pan for at least 30 minutes. By this time they should be firm enough to lift out of the pan using the parchment. Slice and enjoy.
Leftovers: I find these are even better the next day. They firm up and become nice and fudgy, but the crackly crust stays crisp. Give them 10-15 seconds in the microwave if you want to enjoy the leftovers warm.