In a medium bowl, whisk together the flour, the salt, and cocoa powder.

Configure a large sized double boiler. Place the chocolate, the butter, and the instant espresso powder in the bowl of the double boiler and stir occasionally until the chocolate and butter are completely melted and combined. Turn off the heat, but keep the bowl over the water of the double boiler and add both sugars. Whisk the sugars until completely combined and remove the bowl from the pan. Mixture should be room temperature.

Add three eggs to the chocolate/butter mixture and whisk until just combined. Add the remaining eggs and whisk until just combined. Add the vanilla and stir until combined. Do not over beat the batter at this stage or your brownies will be cakey.

Sprinkle the flour/cocoa/salt mix over the chocolate. Using a spatula (DO NOT USE A WHISK) fold the dry into the wet until there is just a trace amount of the flour/cocoa mix visible.

Pour half of the batter into the pan and smooth the top with your spatula. Place the Oreos on top fitting as many as you can. Pour the rest of the batter over the top and smooth the surface.

Bake the brownies for 30 minutes (rotate the pan half-way through baking) and check to make sure the brownies are completely done by sticking a toothpick in. The brownies are done when the toothpick comes out with a few moist crumbs.

Cool the brownies completely before cutting. I like to cut pieces so that each has an Oreo inside.