Preheat the oven to 350 degrees F. Add cupcake liners to two, 12-count cupcake pans and spray them with non-stick spray.
In a large mixing bowl, add the dry ingredients for the cake (flour, cocoa powder, baking powder, baking soda, salt and both sugars). Mix well with a whisk and set aside.
Add the milk and lemon juice (or white vinegar) to a measuring cup and mix well. Let sit for about 5 minutes. (You're basically making a buttermilk substitute by doing this, so if you have buttermilk, you can use that instead and just omit the lemon juice or vinegar.) If the mixture starts looking a little clumpy, it's fine.
Add these liquid ingredients (milk and lemon/vinegar mixture, melted butter, oil, vanilla extract and eggs) to a mixing bowl and whisk well. Do not add the coffee or hot water yet.
Make a well in the center of the dry ingredients and add the liquid ingredients to the bowl. (Not the hot coffee or water yet.) Mix with an electric mixer on medium to medium-high speed just until the ingredients are well combined. Be very careful not to mix too long as that will cause a dense, rubbery and possibly dry cake. Stop mixing once everything is well combined. Generally, mixing longer than a minute is too long.
Scrape down the sides of the bowl and mix again for about only 5-10 seconds more.
Add the hot coffee (or hot water) and mix until well combined.
Again, be careful not to over-mix. Scrape down the sides of the bowl and mix again for about only 5-10 seconds more. Batter will be very thin. That's fine.
Fill cupcake liners about ⅔ of the way full.
Bake at 350 degrees F for approximately 17-20 minutes. Ovens vary. A toothpick inserted into the center of a few cupcakes should come out with either a few moist crumbs on it or clean, but no raw batter. If the toothpick comes out with a few moist crumbs and no raw batter, go ahead and remove the cupcakes from the oven. Overbaking cupcakes will cause them to be dry.
Set the cupcake pans on wire racks to cool for about ten minutes, then take cupcakes out of the pans and let cool completely on the wire racks before adding filing and frosting.