Preheat your oven to 350°F and line a baking sheet with parchment paper. While the oven heats, measure out all your dry ingredients—flour, baking soda, cinnamon, nutmeg, and salt—into a small bowl and whisk them together to distribute the leavening and spices evenly. This ensures even rising and consistent flavor throughout your cookies.

Peel and mash your well-speckled bananas in a large mixing bowl until mostly smooth—a few small lumps are fine and add nice texture. Add the vegetable oil and brown sugar, then mix vigorously for about 2 minutes until the mixture is light, fluffy, and pale. I like to use overly ripe bananas because they're naturally sweeter and require less added sugar, giving the cookies a more authentic banana bread flavor.

Add the egg yolk and vanilla extract to your banana mixture, stirring until fully combined. The egg yolk acts as a binder and adds richness without making the cookies cake-like, which is crucial for achieving the right chewy texture.

Pour the dry ingredient mixture from Step 1 into the wet ingredients and stir until just combined—don't overmix, as this develops gluten and creates tough cookies. The batter should come together loosely with visible streaks of flour still visible when you stop stirring.

Gently fold the chocolate chips into the dough with a spatula until evenly distributed. Let the dough rest for 15 minutes at room temperature—this allows the flour to fully hydrate and helps the dough hold together better when scooping. I find this resting period makes a real difference in cookie structure; they'll be less likely to spread excessively during baking.

Using a cookie scoop or spoon, drop golf ball–sized portions of dough onto your prepared baking sheet, spacing them about 2 inches apart to allow room for spreading. Bake for 10 to 11 minutes until the edges are set but the centers still look slightly underdone—they'll continue cooking from residual heat as they cool, keeping them chewy inside with crispy edges.

Remove the cookies from the oven and let them cool on the baking sheet for 5 minutes so they firm up enough to handle, then transfer them to a wire rack to cool completely. This two-stage cooling prevents them from breaking apart while still allowing steam to escape so they don't become soggy.