In a large heatproof bowl, place your chopped up dark chocolate and peanut butter.
In a medium saucepan, heat heavy whipping cream over medium-high heat until bubbling. Add 4 tbsp butter, 1/2 tsp salt, and espresso powder and whisk until melted.
Pour over your chocolate and peanut butter mixture and wait for 1-2 minutes for the cream to melt the chocolate. Then, stir to combine with a whisk or spatula. Place ganache, covered, in the fridge to chill for at least 2-3 hours or until cool and firm.
Preheat oven to 400°F.
In a large stockpot, combine coffee, 6 tbsp butter, sugar, and 3/4 tsp salt. Cook over medium-high heat until bubbling, about 5-10 minutes.
To your coffee mixture, add the flour and cocoa powder and stir to combine with a wooden spoon. The mixture should come together into a thick ball of dough. Cook for 2-3 minutes to remove the flour taste.
Remove dough from heat and add to the bowl of a stand mixer. Beat with the paddle attachment on medium speed for 5-10 minutes, or until the dough is cool to the touch.
Add your eggs, one at a time, incorporating each fully into the dough before adding the next. You will probably need all four, but the dough consistency should be thick enough to hold its shape but loose enough to form a V shape when hanging from the paddle.
Transfer your choux dough into a large piping bag with no metal tip.
Cut a hole in the tip of the piping bag, about 1" from the tip, and pipe thick eclair shapes on parchment of silicon-lined baking sheets. They should be about 5-6" long and should hold their shape when piped.
Whisk together your last egg and light cream. Lightly brush the tops of the eclairs with your egg wash and place in the oven to bake.
Bake eclairs for 5 minutes, then reduce heat to 375°F and cook for 30 more minutes. After 30 minutes, rotate and bake for 5 more minutes. Leave them in the oven with the temperature off for a few more minutes to help hollow out the insides.
Remove eclairs from oven and chill until room temperature. Poke 3 holes in the bottom of each eclair to let out steam.
Once your ganache is firm and chilled, whip with a whisk or handheld mixer until the ganache becomes light and fluffy.
Transfer ganache to a piping bag with a star tip. Slice off the tops of your eclairs (horizontally) to make thin little caps. Then, pipe your ganache generously on the insides of the eclair.
Garnish with peanut slices and chocolate candies and dust the tops of your eclairs with powdered sugar.