Preheat your oven to 350°F (175°C). Cut the challah bread into bite-sized cubes and spread on a baking sheet. Toast for about 5 minutes until golden and crisp.

In a medium mixing bowl, combine the milk, monk fruit sweetener, cocoa powder, vanilla extract, and beaten egg. Whisk until smooth to create the custard base.

Toss the toasted bread cubes into the custard mixture, stirring gently to coat. Cover and chill in the refrigerator for at least 30 minutes or up to 4 hours.

Grease two ramekins with cooking spray. Layer half of the bread mixture in each ramekin, then sprinkle half of the dark chocolate. Top with remaining bread mixture and the rest of the chocolate.

Place the ramekins in a baking dish and pour hot water until halfway up the sides. Bake at 325°F (160°C) for about 35 minutes until the pudding is set but soft in the center.

Remove from the oven and let cool slightly. Serve warm, optionally topped with whipped topping.