Method

• Preheat the microwave oven at 200°C.
• Butter the sides and bottom of the ramekins. Dust the insides with some cocoa powder. Place the prepared ramekins on a baking tray and set aside.
• Place the butter and chocolate in a microwave oven-safe bowl and melt on medium heat. Set aside to cool.
• In another bowl, beat the egg yolks with sugar using an electric hand mixer. Beat it until it is thick, pale and fluffy. Pour vanilla and fold in the melted chocolate mix.
• In another clean bowl, whip up the egg whites until frothy. Continue to whip until soft peaks form.
• Using a spatula, fold the all-purpose flour into the chocolate mix. Gradually fold in the whipped egg whites. Don’t mix it too much or else the batter will deflate. 
• Divide the batter into the prepared ramekins and bake for 10 minutes in the preheated microwave oven. Bake until the outside of the cake is just set and the middle looks a little wobbly. You might see some cracks on the top but it is nothing to worry about.
• Remove from the microwave oven and let it cool for a minute or two. You can serve the cake in the ramekin itself or run a sharp knife around the edge of the cake and invert on the serving plate. Carefully remove the ramekin and served with some whipped cream, ice cream or enjoy as it is.