Preheat oven to 350° F. Line a cookie sheet with parchment paper or a silicone baking mat.
In a double boiler, or in a medium glass or metal bowl fitted over a pot of barely simmering water, melt the 2 cups of chocolate and butter together. Stir often, should take 3-5 minutes. Remove from heat to let cool slightly.
In a small bowl combine the flour, baking powder, baking soda, espresso powder and salt. Whisk together.
In a stand mixer fitted with a paddle attachment or with a hand mixer, beat together the eggs and brown sugar on medium for 2 minutes.
With the mixer running on low, slowly add in the slightly cooled chocolate mixture followed by the vanilla. Scrape down the sides as needed. Laslty add in the flour mixture and mix just until you no longer see any flour, about 30 seconds. Be sure not to overwork the batter.
By hand, using a wooden spoon or silicone spatula, stir in the peanut butter chips. The batter will be quite loose at this point so let it sit for 5-10 minutes to firm up.
Scoop the batter out using a medium sized ice cream scoop or a large spoon onto the prepared cookie sheet, about 5-6 per sheet. Make sure to space them at least 1 ½ inches apart to account for spreading.
Bake on the middle rack, one sheet at a time, for 10-12 minutes or until puffed and they look slightly shiny and cracked on top. Remove from cookie sheet and let cool fully on a cooling rack.