1. Preheat oven at 160-180 degree C or 350 degree F.
2. Place a large sauce pan on low heat; throw unsalted butter and dark chocolate. Stir, and let chocolate melt. Do not boil it. Remove from heat and allow it to cool for about 5 minutes.
3. Pour beaten egg in pan, a little at a time, stirring after every addition.
4. Add white sugar, sour cream, and plain flour in it. Mix to combine.
5. In a mixing bowl, add cream cheese, and caster sugar. Beat until light and fluffy.
6. Drop 1 egg in mixing bowl. Stir it well.
7. Line a greased baking pan with parchment paper. Spoon half of the chocolate mixture in it. Spread it evenly.
8. Top it with cream cheese mixture.
9. Put the remaining chocolate mixture in the pan.
10. Run a skewer all around to mix the batter.
11. Pop it in oven, and bake for 35-40 minutes.
12. Remove from oven, and allow it to cool for about 30 minutes.
13. Cut in slices and serve brownie with a hot cup of coffee.