Preheat oven to 350 degrees. Microwave butter and pour into a mixing bowl. Add chocolate chips and whisk until melted. If chocolate isn't fully melted, microwave for 15 seconds and continue to whisk until smooth. Set aside.

Add four eggs to the bowl of a stand mixer with the whisk attachment. Add eggs, sugar, brown sugar, sour cream, and vanilla extract. Beat on medium high for 8 minutes, mixture should be light yellow color.

Reduce speed of mixer to low and slowly pour in the melted chocolate/butter mixture. Mix on low for about 5-10 seconds and stop the mixer.

In a separate bowl, whisk together flour, cocoa powder, and salt. Add to batter and fold in just until the flour is combined - do not overmix, it's ok it the batter is slightly chunky.

Spray a 9x13 baking dish with oil or line with parchment paper. Pour half of the batter into the pan. Break about 15 oreos into pieces and spread onto the batter. Add remaining batter on top and then add remaining oreos on top.

Bake for 35 minutes. Allow to cool for 10 minutes before cutting.