preheat your oven to 325 degrees. Spray a 2 quart baking dish with nonstick spray and line the bottom of the dish with cookies. You may need to break a few in half to fill in the corners of the dish. Set aside.
In a small bowl combine cocoa powder, flour, espresso powder & salt. Whisk together until combined.
In a separate large bowl, combine eggs and sugar and beat with an electric mixer on medium speed for 5 to 7 minutes, the mixture should be thick and pale yellow. Add vanilla and flour mixture into the egg/sugar mixture and SLOWLY beat on low speed for a few minutes, until combined (no lumps). Add in the melted butter and continue to beat on low speed just until everything is combined with no streaks of butter, do not over mix.
Pour batter over the Oreos and smooth out evenly in the baking dish. Optional: *see note* place the baking dish into a larger casserole dish and place in the oven, pour hot water into the casserole dish (about 1 inch high of water) to create a steam bath. Bake for 1 hour
Carefully remove the baking dish from the water bath. Allow the pudding to cool for about 10 to 15 minutes before serving, serve with ice cream.