1tablespooncoarse granulated sugar, for topping (optional)
Preheat the oven to 350ºF and line a 9-inch square baking dish with parchment paper. In the bowl of a large food processor fitted with an "S" blade, combine the black beans, flour, oil, sugar, ginger, cinnamon, cloves, salt, baking soda, vanilla, molasses, and vinegar. Process until a smooth batter is formed.
Pour the batter into the lined baking dish and sprinkle the top with the tablespoon of coarse sugar, if desired. Bake until the top feels firm to a light touch, about 25 to 30 minutes. Cool completely before removing the bars from the pan and slicing.
These bars will keep well at room temperature for up to 48 hours tightly covered, but for best shelf life keep them in an airtight container in the fridge for up to a week.