1. Preheat the oven to 350ºF. Spray ramekins with non-stick cooking spray. In microwave safe bowl or double boiler, melt the chocolate with the butter until smooth. If using the microwave, stir every 30 seconds to avoid burning. Once smooth, remove from heat to cool slightly.
2. In a large mixing bowl, beat sugar and egg yolks until thick and pale, about 3 minutes on high-speed with an electric hand mixer.
3. In a separate large bowl with clean beaters, beat the egg whites into stiff peaks. Fold the egg yolk and sugar mixture into the chocolate. Fold in half the egg whites. Once almost combined, fold in remaining egg whites. Fold in the flour until combined.
4. Divide pudding mixture between ramekins. Arrange ramekins on a baking sheet and bake for 15 minutes until puddings have puffed up. Gently, remove from oven and transfer onto plates. Garnish with a dollop of whipped cream or scoop of vanilla ice cream.