Preheat the oven to 180C or 365F.
In a medium mixing bowl, combine the 1/2 cup plant milk for the loaf and the vinegar, and set aside to form a buttermilk. Don't panic if it looks curdled and awful - that is the whole idea. It will create a light and fluffy loaf. Thanks buttermilk.
In a large bowl, mix together all the dry ingredients - flours, spices, sugars and baking powder/soda.
Back to the buttermilk: add the remaining wet ingredients - pumpkin puree, eggs and oil. Whisk until a batter has formed.
Add the dry ingredients into the wet, and stir thoroughly to combine. The batter should be smooth, and look slightly aerated, thanks to the combination of 'buttermilk' and baking soda.
Pour the batter into a silicon nonstick loaf pan. I like to give my silicon pans a little spray of oil first, even though you're not really supposed to. Rule breaker etc etc.
Bake the loaf from 45 minutes to an hour. Mine needed the whole hour, and I covered them with a bit of foil towards the end, because the top looked perfect at 45. Once it's cooked, allow it to cool for 10 or so minutes before transferring to a wire rack to cool completely.