Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper or a silicone baking mat.
- In a large mixing bowl, beat together the softened butter and granulated sugar until light and fluffy, about 2-3 minutes.
- Add the egg, vanilla extract, lime zest, and lime juice, mixing until well combined.
- In a separate bowl, whisk together the all-purpose flour, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
- For the graham cracker topping, mix together the graham cracker crumbs, sugar, and melted butter in a small bowl until the mixture is evenly combined and crumbly.
- Scoop about 2 tablespoons of cookie dough and roll it into a ball. Place the dough balls onto the prepared baking sheet, spacing them about 2 inches apart.
- Gently press a small amount of graham cracker topping onto the top of each dough ball, pressing lightly so it sticks.
- Bake for 9-11 minutes, or until the edges are golden brown and the centers are set. The cookies will remain soft and chewy in the center.
- Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.
- For the glaze, whisk together the powdered sugar, fresh lime juice, and vanilla extract in a small bowl until smooth and pourable. Adjust the consistency by adding more powdered sugar or lime juice, if needed.
- Once the cookies have cooled, drizzle the lime glaze over the top of each cookie.
- Allow the glaze to set for a few minutes, then serve and enjoy the refreshing flavors of Key Lime Pie Cookies!