Preheat oven to 160 degree C. Line a 18 cm square baking pan with parchment paper and grease it well with oil.

Now take dark chocolate and butter in a heat proof bowl and melt it over a pan of simmering water till the chocolate is melted.

Add in powdered sugar and mix well.

Add in eggs, one at a time. and whisk well.

Sieve in cocoa powder and flour. Mix well.

Spoon this into the pan and bake for 40 to 45 mins till a toothpick inserted comes out clean.

Now remove it and let it cool for 15 mins.

Now remove it carefully from pan and cool completely.Slice and serve.