Mix the milk and vinegar in a measuring cup and set aside for 5 minutes (the milk will thicken and sour to the consistency of buttermilk).
Meanwhile, mix the flour, oats, baking powder, baking soda, salt, and sugar in a medium bowl.
After 5 minutes is up, crack an egg into the milk mixture and beat.
Add egg mixture to dry ingredients, stirring until just combined (do not overwork the batter!)
Fold 1 cup of berries into the batter gently.
Heat a heavy or cast iron skillet / griddle and cook pancakes in melted butter in 1/3 cup amounts over medium heat. Flip when slightly browned around edges and bubbles form at the top.
Serve with extra berries and maple syrup.