Heat the oven to 200°F, and set a large rimmed baking sheet on the center rack.
Melt 3 Tbs. of the butter and let cool slightly. In a large bowl, combine the butter with the mashed banana, buttermilk, eggs, and vanilla.
In a medium bowl, whisk the flour, sugar, baking powder, baking soda, salt, nutmeg, and cinnamon. Pour the dry ingredients over the wet and fold together with a spatula until just incorporated; let sit for 5 minutes.
Heat a griddle or large nonstick skillet over medium-low heat until drops of water dance briefly before evaporating. Lightly butter the griddle. Working in batches, and buttering the griddle as necessary, pour a scant 1/4 cup of batter onto the griddle for each pancake, spreading a little to make 4-inch circles.
Cook, undisturbed, until the edges look dry and the underside is golden brown, about 3 minutes. Flip and cook until the second side is golden brown, about 3 minutes more. Transfer to the baking sheet to keep warm.
Melt 1-1/2 Tbs. of the remaining butter in a 10-inch nonstick or cast-iron skillet over medium heat. Add half the banana slices and cook until browned, about 3 minutes per side. Repeat with the remaining butter and bananas. Serve the pancakes topped with the caramelized banana slices and warm maple syrup.
Mothers Secret Recipes of Comfort Food & Culinary Inspiration from an Organic and Allergen-free Approach