Preheat your oven to 300 degrees and line a baking sheet with parchment paper. This will be to keep your finished pancakes warm while you cook the rest of your batter.
In a large liquid measuring cup or a bowl, stir together the milk and vinegar. Let it sit for a few minutes - the milk will start to thicken and slightly curdle. This will be your buttermilk.
Coarsely chop your chocolate and set aside. In a large bowl, whisk together the flour, sugar, baking powder, baking soda, salt, and pumpkin pie spice.
In a separate large bowl, whisk together the buttermilk, pumpkin puree, butter, vanilla extract, and egg until well combined. Pour the wet ingredients into the dry ingredients and whisk until a batter forms. A few small lumps in the batter are okay.
Add the chopped chocolate and fold together until evenly incorporated throughout the batter. Let the batter rest for 5-10 minutes - this step is critical for the fluffiest pancakes!
Heat up your non-stick pan or griddle to low-medium heat. If your pan is truly non-stick, you don’t need to grease it with anything. But if you want to just to be safe, use vegetable oil and wipe up any excess oil with a paper towel.
Use a cookie/ice cream scoop or ladle to spoon the batter onto your pan (I usually do about ¼ cup per pancake), cooking only a few at a time as to not overcrowd the pan. Let the pancakes cook for 1-2 minutes on one side until the edges are completely set and there are bubbles on the surface.
Carefully flip your pancakes and cook for an additional minute or so. Place the pancakes on the prepared baking sheet and into the oven to stay warm.
Repeat this with the remaining batter, adjusting the heat if necessary.
Top the finished pancakes with maple syrup, chopped nuts, whipped cream, fruit, etc., and dig in!