Make the vegan buttermilk by stirring together dairy-free milk and apple cider vinegar. Set aside to curdle.
Whisk the dry ingredients together in a medium size mixing bowl.
Mix the muffin batter in a large mixing bowl. Using a wooden spoon, beat the softened butter and the brown sugar together until creamy and incorporated.
Add the pumpkin puree and vanilla - mix until smooth.
Add ½ the dry ingredients and ½ the buttermilk to the pumpkin mixture: fold together. Add the remaining dry ingredients and buttermilk - stir just until incorporated being careful not to over mix. Fold in any add ins at this time. Let the batter rest while you preheat the oven.
Preheat the oven to 425º F and prepare a 12 cup muffin tin by rubbing each cup with dairy-free butter/margarine over the sides and bottom. Alternatively use paper liners or spray with cooking spray. Make streusel if using.
Once the oven is preheated, scoop the batter into the prepared muffin cups, filling almost to the top. For slightly larger bakery-style pumpkin muffins, fill only 11 spots (as I did in the photos). Sprinkle pumpkin seeds or streusel over the top gently pressing into the batter. Then pop into the oven.
Bake at 425° F for 7 minutes and then reduce the heat to 350° F for an additional 10-12 minutes or until a toothpick comes out clean. Let cool for 5 minutes in the pan then transfer the muffins to a wire rack to finish cooling.
Once cool, drizzle with frosting if using.