Whisk together milk, sour cream, butter, vanilla, and eggs in a large bowl until smooth.
Add in bisquick, brown sugar, baking soda, salt, and cinnamon and mix until *just combined*.
Set aside for 10 minutes to rest.
Optional: lightly grease (using cooking spray, oil, ghee, or butter*) a griddle or non-stick pan*, then heat over medium heat.
Once hot, scoop the batter using a 1/4 cup measuring cup onto the pan, sprinkle with mix-ins (such as chocolate chips) if desired, then cook until bubbles form and the edges are dry, about 2 to 3 minutes.
Flip and cook until browned on the other side, then repeat with remaining batter (reduce heat, if necessary, to avoid over-browning).
This recipe was tested with Bisquick Original which calls for 2 cups mix, 1 cup milk, and 2 eggs to make pancakes.*See Best Method for Cooking for pan (cast iron vs griddle, etc.) and fat (oil vs butter, etc.) suggestions.