Combine milk and vinegar in a bowl. Let it sit for 5 to 10 minutes until thick and curdled.
Prepare the dry ingredients by mixing flour, baking soda, and salt in a medium bowl. Set it aside.
In a large bowl, mash bananas with a fork.
Add brown sugar, eggs, oil, vanilla, and clabbered milk (milk+vinegar mixture). Whisk until combined.
Add dry ingredients to the wet ingredients. With a rubber spatula, mix until just combined or no more flour is visible. Do not overmix. If you're adding extras, fold them in at this point.
Pour the batter into the pan and smooth it out.
Sprinkle a good amount of turbinado sugar on top.
Bake in a preheated oven of 350° F (177° C) for 55 to 60 minutes until the top is browned and slightly domed with the inside peeking through. When you insert a toothpick or thin-bladed knife in the center, it should come out with a few crumbs.
Let it cool for 15 minutes in the pan. Enjoy it warm with some butter.
Notes
Milk + vinegar (or lemon juice): This combination makes clabbered milk or essentially buttermilk in a pinch. Sour cream and plain Greek yogurt (full-fat or reduced) work just as well.
All-purpose flour: You can substitute up to 50% with white whole wheat flour or make it gluten-free with almond flour.
Oil: I used melted coconut oil in this recipe. You can substitute 1:1 for other fats like canola oil, vegetable oil, or melted butter.
Turbinado sugar: An optional ingredient, but adds texture and a slight crunch. You can also use (as a mix-in or topping) chopped nuts like walnuts or pecans, chocolate chips, raisins, or spices like cinnamon or nutmeg.