In a double boiler over low heat, melt butter and dark chocolate together and remove from heat. When it's cooled add eggs and vanilla extract.

In a separate bowl combine all dry ingredients, seive and then add to the butter mixture. Pre heat the oven (I used convection oven to 300°F). Butter the baking tray and pour the mixture.

Sprinkle the chopped walnuts and bake for 40 mins. Check by inserting a pick or knife if it's baked.

Brownie is ready to serve warm or cold.

Note: You can also use chocolate chips. If you are not using convection then set the temperature according to your manual or convert it in using converter.