Preheat oven to 175C.
Line pan with aluminium foil and lightly grease pan.
On a bain marie / double boiler, melt chocolate and butter. Whisk until smooth.
Allow to cool for 5-10 minute.
In a clean mixing bowl, melt cream cheese and sugar over a bain marie.
Whisk till cheese is smooth, remove from heat, then whisk in vanilla extract until combined.
Now your chocolate mixture should be cool enough. Add eggs, espresso powder, vanilla extract, salt, and sugar. Whisk until very well combined
Add flour, and 3/4 of the oreo pieces. Mix till just combined. Careful not to overmix!!
Pour half of the brownie mixture into the pan. Use a spatula to carefully spread it out evenly.
Next, slowly pour in the cream cheese mixture and even out the top as much as you can.
Pour in the remaining half of the brownie mixture, and sprinkle the reserved oreo pieces over the top.
Bake for 30-35 minutes until top of the brownie is set.
Allow to cool completely in pan.