Preheat the oven to 350° F.
If you are using them, mold the 2 disposable aluminum pot-pie pans into triangular ear shapes, raising the edges of the pans up [think of it as lifting up a collar] so that they will be as tall as your other pans and hold more batter.
Spray each baking pan with baking spray.
Line the bottoms of each pan with parchment paper cut to size.
[Trace around the bottoms of the pan with a pencil to create a guide.]
Spray the tops of the parchment with a bit of baking spray.
Sift the flour, cocoa powder, baking soda and baking powder into the bowl of an electric mixer using a sifter or a wire-mesh strainer.
Add salt and sugar to the bowl, and with the mixer set to low speed, beat for 30 seconds or so until combined.
In a separate bowl, whisk eggs, buttermilk, oil, and vanilla.
With the mixer set to low, add the wet mixture to the dry mixture and blend until just combined.
Place the peanut buter in a large measuring cup and pour coffee over top.
Whisk tihs mixture until the peanut butter is melted and fully blended with the coffee.
Beat the coffee & peanut butter mixture into the cake batter until fully incorporated.
You will have about 6 generous cups of batter when completed.
Pour about 3-3.5 cups of batter into the largest pan, 1-2 cups of batter into the smaller pan, and less than 1 cup of batter into each of the small tins for the ears.
Look to see that the level of batter is even in each of the pans. Adjust accordingly.
Set the filled pans in the middle rack of your oven.
Bake cakes for a total of about 30 minutes, until a butter knife inserted into the centres of the cakes comes out clean.
[Today, our smaller cakes took 28 minutes, and our larger cake took 32 minutes.]
Cool the cakes in their pans on top of wire racks for at least 30 minutes.
Then, invert the cakes on the wire racks, remove the parchment circles, and cool completely.