Preheat the oven to 180 degrees Celsius.
Line a baking tray, and lay your bananas on it with a light spray of oil. Once the oven is ready, cook the bananas for 20-30 minutes. If they're super ripe, they'll probably only need 20, but the firmer ones will need longer.
While the bananas are cooking, mix together the soy milk and vinegar, and set aside to form buttermilk. It should be clumpy and separated by the time you stir it into the mixture - aside from contributing to the fancy name it will also give the muffins lift.
In a large bowl, mix together the dry ingredients and set aside.
Once the bananas are cooked - they smell like heaven and they're super squishy, transfer them to a bowl and mash them roughly. Allow them to cool slightly so your batter doesn't become scrambled eggs.
Once the bananas have cooled, add the wet ingredients (buttermilk, eggs, mashed banana, olive oil and vanilla bean paste) to the dry, and mix thoroughly to combine. After a couple of minutes, the batter should be spoonable but also kind of fluffy looking.
Grease 10-12 muffin holes (depending on their size) with a good spray of olive oil, and use a spoon or ladle to fill them with batter. Top them with the extra banana slices, and a sprinkle of brown sugar and/or cinnamon, if you fancy. Allow them to cook for 20-25 or so minutes - I like to finish mine with a quick blast under the grill for some colour on top.