Melt the chocolate and butter together (double boiler or microwave). Stir until well melted.
In a separate bowl, beat together the sugar and eggs until thoroughly combined. Add the espresso powder (optional), vanilla, baking powder and salt, then stir into melted chocolate, mixing well.
Stir in the flour. Let the batter sit for at least 5 minutes to thicken; it should be the consistency of thick cake batter.
Drop the cookie dough in round blobs onto a parchment-lined or greased baking sheet. Leave about 2 inches in between dough balls (mine were never "balls" but more liquidy). You may place a nonpareil or kiss in the middle, if desired (I didn't).
Bake for 10 to 12 minutes,until the tops are shiny and cracked. You want them to bake all the way through but just barely; additional baking time will make them cakey and not fudgy.
Remove cookies from oven, wait 5 minutes and then transfer to wire rack to cool.