325* oven. Grease an 8" baking pan and set aside. (Note: the original recipe says to line the pan with parchment paper. Your call. I did not).
Melt chocolate and butter in the top of a double boiler and stir to combine. I use a bowl that sits above the pot of simmering water (the water DOES NOT touch the bowl).
Turn off the heat. Add the granulated and the dark brown sugar to the melted chocolate and butter mixture. It won't be smooth.
Remove from the heat and let cool 3-5 minutes (adding eggs to the hot mixture would cause thin white strings of egg in your finished product, since the heat would cook the egg white).
Meanwhile, whisk together the flour, cocoa powder, salt, and espresso powder.
Slowly add the eggs to the chocolate and sugar mixture. I set the eggs in a liquid measuring cup, beat them, then drizzled them into the mixture, while stirring with my other hand.
Add in vanilla extract.
Fold in flour mixture to the chocolate and sugar mixture JUST until combined. When you see a couple of floury streaks, tread slowly: You are almost done mixing!
Spread batter into the greased pan.
Bake for 50-55 minutes or until a wooden pick inserted in the center comes out with a few crumbs. Leave, cooling, in the pan for 15 minutes. If you used parchment paper, remove the brownies from the pan, cool completely on a wire rack, and then store in the refrigerator for up to 6 days.