Heat butter and chocolate in a bowl till chocolate melts.
Remove from heat.
Add sugar and whisk till combined.
Add vanilla extract and mix.
Let the mixture cool for 5 minutes.
Add eggs, one at a time and mix well.
Add flour and mix nicely.
Now add the crushed cookies in the batter ( keep a few for placing on top ) and pour the batter in the prepared pan.
Top the batter with a few cookie pieces.
Bake for 25-30 minutes.
Remove from oven and let it cool completely.
Cut into square pieces.
You can warm the brownie for a few seconds in a microwave before serving and also a scoop of vanilla ice cream is a great combination with these brownies.
You can replace semi-sweet chocolate with dark chocolate if you wish.Don't over bake the brownies, if you like the gooey texture in between.Let the brownies cool down properly, before slicing them.Do not crush the Oreo biscuits, break them with your hands in relatively medium pieces.Once your brownies are ready, let them cool down fully to room temperature, as they take a little time to set. If you simply cannot wait, just put the baking tray in the fridge for some time, slice it and enjoy it. This will fasten the cooling process.You can also add chocolate chips or white chocolate chips in the batter for extra texture. The added chips will give you a crinkly top.Once the baking time of 25-30 minutes is over, check on them, give the baking tray a shake, if they jiggle they need a little more time to get ready. If they don't, they are ready.Also do not over bake the brownies, it will make them hard and won't taste good. They should be a little gooey from the middle.Always use high-quality chocolate and do not forget vanilla extract to make these brownies.