Preheat the oven to 450°F with one oven rack placed in the center of the oven, and another about 6 inches below the broiler.
Prepare a (half-sheet sized) sheet pan by lightly spraying with baking spray and lining with parchment paper.
In a large bowl, whisk together the flour, baking powder, baking soda, salt and sugar.
Cut the butter into the flour using a pastry cutter, two forks, or a food processor until you have coarse crumbs.
Whisk together the kefir (or buttermilk) and eggs, and stir into the flour. Do not overmix, you should have some lumps.
Spread the batter into the prepared pan using an offsest spatula and very gently shaking the pan. Top with the sliced bananas.
Stir together the cinnamon and sugar and sprinkle about half of the mixture over the bananas. Place the sheet pan in the oven to bake for about 8-10 minutes, or until golden brown and a toothpick inserted in the center comes clean.
Sprinkle a little more cinnamon sugar on top and transfer to the broiler for a minute or two. Keep a close eye on it so that it doesn't burn!
Remove from oven, let it rest for a few minutes, then slice and serve with your favorite toppings!
Should I use kefir or buttermilk? I love either option in this recipe. Buttermilk is, of course, makes for a traditional pancake, and if you do use buttermilk, be sure to use a good quality, thick buttermilk. I personally love Clover buttermilk. However, I also love kefir - the consistency is similar to buttermilk, and this fermented milk is rich in probiotics.
What is the easiest way to spread the batter? I like using a large offset spatula. Be gentle with the batter and do not tap the batter in the pan to help keep the pancake as fluffy as possible.
Can the pancakes be frozen? Yes! Cool the pancakes completely on a wire rack. Store the pancakes with a sheet of parchment or wax paper between each pancake in a freezer-safe container. This will make it easy for you to separate one pancake and reheat it!
How to reheat frozen pancakes: The easiest way to reheat frozen pancakes is in the microwave. Place between 1-4 pancakes on a microwave-safe plate and cover with a damp paper towel. Reheat in 20-second increments until warmed through.