Preheat oven to 325°F (165°C) and line baking sheets with parchment paper.

Whisk together flour, baking soda, espresso powder, cinnamon, and salt in a medium bowl.

In a large bowl, cream together the melted butter, brown sugar, and granulated sugar until fully combined.

Beat in the egg, egg yolk, and vanilla extract until the mixture is light and creamy.

Gradually add the dry ingredient mixture to the wet ingredients, mixing until just combined to avoid gluten over-development.

Manually fold in the chocolate chips using a spatula.

Drop rounded tablespoons of dough onto the prepared baking sheets, spaced approximately 2 inches apart.

Bake for 10 to 12 minutes until the edges are lightly browned but the centers remain soft and slightly underbaked.

Cool on the baking sheet for 5 minutes before transferring to a wire rack to ensure the gooey center sets properly.