Mix all the wet ingredients in a blender or food processor.
Mix the dry ingredients in a big bowl. Add the warming spices if using.
Add the wet ingredients to the dry ingredients and combine with a spatula until incorporated.
Add the chopped walnuts and combine.
Fill the muffins cups and decorate with walnuts.
Preheat the oven to 350F / 170C and bake for 60 to 70 minutes, or until the muffins are no longer soft to the touch. Allow the muffins to rest on a cooling rack before serving.