In a large mixing bowl, combine cooled melted butter with brown sugar. Blend the ingredients until creamy (2-3 minutes).

Add mashed banana, egg yolk, and vanilla extract. Stir continuously until thoroughly mixed (1-2 minutes).

Sprinkle salt, baking soda, and optional cinnamon into the mixture. Stir gently until fully incorporated (about 1 minute).

Gradually add all-purpose flour, folding it in; avoid overmixing (about 1-2 minutes).

Fold in the chocolate chips until evenly distributed (about 1 minute).

Cover the bowl and refrigerate the dough for at least 30 minutes to prevent spreading.

Preheat your oven to 350°F (175°C) while the dough chills.

Drop spoonfuls of dough onto prepared baking sheets, spacing them 2 inches apart. Optionally, add extra chocolate chips on top.

Bake for 10-12 minutes until edges are golden brown but centers remain soft. Monitor carefully.

Let the cookies cool on baking sheets for 2 minutes before transferring them to wire racks.