For the cornbread: Preheat the oven to 400 degrees F. Generously spray a 12-cup muffin pan with cooking spray.
Whisk together the cornmeal, flour, sugar, salt and baking soda in a medium bowl. In a separate small bowl, whisk together the buttermilk, egg and butter. Pour the buttermilk mixture into the cornmeal mix and whisk until incorporated. Divide the batter evenly between the prepared muffin cups (1 tablespoon plus 1 teaspoon per cup). Rap the muffin pan on the counter several times so the batter spreads evenly in each cup.
Bake until slightly domed on top and golden brown on the underside, about 10 minutes. Cool completely in the pan. Hold a paring knife at an angle to cut a conical shape out of the top of each muffin so that the base is like a shallow bowl. Reserve the cut-out tops.
For the chili: Heat the oil in a medium skillet over medium-high heat. Add the beef and 1/4 teaspoon salt and cook, breaking up any clumps with a wooden spoon, until brown, about 5 minutes. Reduce the heat to medium and add the onion and chili powder. Cook, stirring occasionally, until the onion is softened, about 5 minutes. Add the tomato paste and cook, stirring, 1 minute. Add the chocolate and 3/4 cup water and simmer, stirring occasionally, until most of the liquid has cooked off, about 10 minutes. Keep warm or reheat before serving.
Make the bites: Reheat the cornbread if desired (the best way is in the microwave 1 to 2 minutes to avoid drying them out). Divide the chili evenly between the cornbread cups and top with a sprinkling of cheese and scallions. Place the cornbread top on top and serve warm.