For Brownie Layer:
On medium heat, in a big saucepan, melt butter. Once slightly melted, take off heat and stir to melt it fully. Add cocoa powder, sugar and whisk well till incorporated.
Remove from the stove, it should not be too hot. Whisk in eggs quickly along with vanilla.
Finally add flour and salt, coffee liquor, whisk well - for 3-4 minutes and keep aside.
For Cookie Dough Layer:
In a large bowl, using hand mixer, cream butter and sugars for 3-4 minutes.
Add vanilla extract, egg and whisk again for a minute or so.
Add the flour, salt and fold in with a silicon spatula.
In the end fold in the chocolate chips.
Oreo Layer:
Roughly 20 Oreo or Dark Fantasy cookies, if you get double stuffed Oreos, choose those, with the Vanilla filling as the white stands out in the dark brownie. I used a mix of choco filled and vanilla filled cookies, but next time will stick to vanilla alone.
Assembly
Line a 9X9 inch pan with parchment or aluminium foil. Butter or grease with oil.
For Cookie Layer : Put the cookie dough on the greased lining of the tin and spread it well to the corners, in a uniform layer.
Oreo Layer : Place the cookies side by side covering the cookie dough entirely. Break the cookie in half, if you want to cover a little bit of extra space.
Brownie Layer : Top the Oreos with the Brownie batter smoothening it out right upto the edges with a silicon spatula.
Bake for 30-35 minutes, until tester comes out clean.
Remove from over and cool outside removing it along with parchment / foil on a cooling rack - for one hour.
Cut into 16 squares.
Serve as it is, slightly warm or with vanilla ice cream.