1. Preheat the oven to 350 degrees . Whisk together flour, sugar, cocoa powder and baking soda in a medium bowl. In another medium bowl, whisk together egg, milk, applesauce, vegetable oil, ground cinnamon, vanilla extract and sea salt. Make a well in the center of the dry ingredients and gradually whisk in egg mixture until smooth; divide batter among eight oven-safe mugs or ramekins. Break bittersweet chocolate into 8 pieces and press gently into the center of each mug. Bake 20 minutes or microwave one at a time until puffed and just set in the center, 35 to 40 seconds. Dust with powdered sugar if desired and serve warm.