Combine the milk and vinegar in a medium bowl, stir, and set aside for 5-10 minutes to slightly curdle.
In a large bowl, add the flour, baking powder, baking soda, salt, sugar, pumpkin pie spice, and whisk to combine.
To the buttermilk, add the pumpkin puree and vanilla. Whisk together until well combined. Drizzle in the melted vegan butter and stir until just combined.
Pour the wet ingredients over the flour mixture and fold with a wooden spoon until just combined. Do not overmix - lots of lumps are fine. Allow the batter to rest for 10 minutes.
Heat a nonstick frying pan over medium-low to medium heat for several minutes. To test if the pan is hot enough, throw a couple drops of water into the pan - if they sizzle as soon as they hit the pan, the pan is ready. Add a touch of cooking oil and distribute evenly with a paper towel so there’s just a thin film of oil.
Ladle ½ cup pancake batter into the pan. Cook until the bubbles become rather uniform in the center and the edges of the pancakes start to dry out and brown, about 1 ½ to 2 minutes.
Carefully flip and cook on the second side until golden brown, 1 ½ to 2 minutes. Store cooked pancakes on a heatproof tray or plate, each pancake separated by a sheet of parchment paper. If desired, keep warm in the oven at 200ºF while you make the rest of the pancakes.
Repeat with the remaining batter, adding a touch more oil to the pan as needed to cook the pancakes.
Serve pancakes warm with a pat of vegan butter, if desired, and maple syrup.