Preheat oven to 180 degrees Celsius (350 degrees Fahrenheit).
Peel the bananas and place in a wide-bottomed bowl, then use a fork to mash until you get a smooth paste.
Place the coconut oil in a separate large bowl and melt over a saucepan of boiling water or in the microwave (skip this step if using any other oil).
Once melted, add the vinegar to the same bowl along with the salt (and cinnamon if using) and ground almonds.
Sift in the flour, baking powder and bicarbonate of soda.
Add the mashed bananas, and mix well, adding the milk a small amount at a time until you get a loose batter. You may not need to use it all depending on how liquidy your bananas are - you may also need to add a little more milk if your bananas are dry.
Add the blueberries and fold them in gently to make sure you don’t crush them.
Transfer the mixture between muffin cases in a muffin tin.
Bake in the oven for 20 minutes until risen and an inserted skewer comes out clean .
Tastes best when fresh, but keeps covered in the fridge for up to a few days - reheat in an oven toaster if you like.