In a small bowl, mix together the milk and vinegar and set aside to "sour".
In a large bowl, mix together the flour, powdered sugar, cornstarch, baking powder and salt. Create a well in the centre.
Add in the eggs, pumpkin puree, butter and soured milk. Mix until smooth.
Heat a large skillet over medium heat and spray with cooking spray. Scoop 1/4 cup of batter for each pancake and flip when bubbles are covering the surface of the pancakes. Flip and cook the other side until it is golden. Repeat for the remaining pancakes.
Notes
You can substitute buttermilk for the milk and vinegar combo.