Set your frozen cherries in the fridge to thaw overnight or for at least a day. Make sure to add the frozen cherries to a colander to drain the juice and add a bowl under it to collect the juice. Do not throw away the juice. Add it to a bowl and keep it chilled until ready to use it later.
Take out one cup of the defrosted cherries and mash them up very well. Drain off the juice. Save that juice with the other you drained from defrosting the cherries. Set the bowl of mashed cherries aside as you'll use that for your cake batter.
Preheat the oven to 350 degrees. Grease and flour three 8 inch round pans. (If you only have two pans, don't try to bake all the batter in only two pans, it's too much.) (Just pour a 1/3 of the batter into each of your two pans and chill the rest of the batter covered while your cakes bake. Once they're baked and removed from their pans, clean one of your pans and then bake the remaining batter in it.)
In a large mixing bowl, add the dry ingredients: The all purpose flour, unsweetened cocoa powder, baking powder, baking soda, salt, packed brown sugar and granulated sugar. Whisk well and set aside.
In another bowl add the liquid ingredients: The softened butter, oil, extract, buttermilk, eggs and the mashed cherries (do not add the warm coffee yet). Mix well.
Do not worry if your butter clumps up a bit. It will be fine. Just keep going.
Pour the liquid mixture into the dry ingredients and mix on medium just until combined.
Add the warm coffee and mix again just until everything is well combined. (You can add the coffee in two parts so that the batter doesn't splash.)
Don't mix the batter for several minutes, that's too long. Stop mixing once everything is combined well.
Scrape the sides and bottom of the bowl and mix again for about 10 seconds.
Add the mini chocolate chips and mix in by hand.
Pour into three greased and floured 8 inch round pans and bake at 350 degrees F for approximately 35-40 minutes. (See above if you only have two pans.)
Set on wire racks to cool for about ten minutes, then turn out the cake layers onto the racks and remove from the pans to cool completely.
Make sure your cake layers are cooled completely before assembling.