Preheat the oven to 180 C

Place the chocolate pieces and the butter in a small saucepan. Place the sauce pan inside another bigger saucepan with simmering water. Stir often until chocolate and butter are melt and blended. Do not overcook. Let cool aside.

Separate the egg yolks from the egg whites. Reserve the egg yolks. Beat the egg whites with vanilla until they rise and become foamy.

Transfer the chocolate and butter mix to a bowl, stir in the egg yolks and beat well.

Then add in the sugar and flour and keep on mixing until smooth.

Slowly incorporate the egg white into the chocolate mixture until firm.

Brush with butter the bottom and sides of a baking pan. Then sprinkle with flour all over.

Pour the chocolate mixture into the greased baking pan and bake in the oven for 20 minutes. Make sure not to overcook; the inside of the cake should be warm and moist.

Serve warm with vanilla ice cream on the side.