1. Preheat the oven to 180C and grease a 12 hole muffin pan with oil or butter.
2. If you are making the optional peanut buttercream to top the muffins, start by making it. Measure the coconut oil and peanut butter into a bowl. Heat in the microwave for 20 seconds until the peanut butter melts. Alternatively, melt in a saucepan over a low heat. If using a saucepan, transfer the melted peanut butter mixture to a mixing bowl and sift in the icing sugar (or sift the icing sugar into the bowl that has been in the microwave). Whisk for 30 seconds to combine, then whisk in the vinegar. Cover and chill in the fridge for an hour until set.
3. Mix the flaxseed with 6 tablespoons of warm water and set aside.
4. Sift the flour and baking powder into a mixing bowl and add the sugar and cinnamon. Mix to combine.
5. In a separate bowl, use a whisk to mix the peanut butter, pumpkin puree and oil together with 25ml water and the flax seed mixture. Fold the peanut butter mixture into the flour using a spatula until no dry spots are visible. If the dough looks very dry (depending on the pumpkin puree), add a couple tablespoons of dairy free milk. Scoop heaped dessert spoons of the mixture into the cupcake holes. Place in the oven to bake for 15 minutes.
6. Remove from the heat and allow to cool completely before spreading on the peanut butter cream.

The muffins will keep in an airtight container for up to 3 days.