Preheat the oven to 325°F. Spray a 9x5-inch loaf pan with nonstick cooking spray or line with parchment paper for easy removal.
Melt the butter and set aside to cool slightly.
In a large bowl, mash the bananas with a fork until mostly smooth.
Add the melted butter, honey, egg, and vanilla. Whisk together until fully combined.
In a separate medium bowl, whisk together the flour, baking soda, baking powder, and kosher salt.
Add the dry ingredients to the banana mixture. Stir gently with a spatula or wooden spoon until just combined. Do not overmix.
Pour the batter into the prepared loaf pan and smooth the top.
Bake for 65 to 75 minutes. About 40 minutes into baking, check the bread. If the top is browning too quickly, loosely cover it with aluminum foil to prevent burning while the center finishes baking.
Bake until a toothpick inserted into the center comes out with a few moist crumbs but no wet batter.
Remove from the oven and let the bread cool in the pan for 10 to 15 minutes. Then transfer to a wire rack to cool completely before slicing.