Combine the milk with the vinegar (or lemon juice) in a bowl and set aside for 10 minutes to "sour." In a large bowl, combine the dry ingredients.
Meanwhile, add the coarsely chopped strawberries, sugar, and balsamic vinegar together in a bowl and mix. Let stand until the strawberries become slightly broken down and release their sugars and juices, about 10 minutes.
Whisk the egg, melted butter, and vanilla into the "soured" milk, and then add it to the dry ingredients. Whisk well to form a smooth batter. Make sure all the lumps are gone. Let the batter rest for 30 minutes before using. It will get thicker as it rests.
Heat a skillet or griddle over medium heat and coat with the cooking spray. Pour ¼ cup full of batter for each pancake onto the skillet and cook until bubbles appear on the surface. Flip and cook until light golden brown. Serve with the strawberries and a drizzle of maple syrup.