Preheat the oven to 350°F (175°C) and lightly grease a baking sheet or line with parchment paper.

To prepare the lime curd, whisk together the beaten egg, granulated sugar, and lime juice in a medium saucepan while still cold. Place over medium heat and cook, whisking constantly, until the mixture thickens and begins to bubble, about 10 minutes. Remove from the heat and strain through a fine-mesh strainer into a bowl. Whisk in the lime zest, press plastic wrap directly onto the surface, and refrigerate until completely chilled, about 1 hour.

In a large bowl, beat the softened butter and brown sugar until light in color and fluffy, about 3 minutes. Add the egg and vanilla extract and mix until smooth.

In a separate bowl, whisk together the graham cracker crumbs, flour, baking powder, baking soda, kosher salt, and cinnamon. Add the dry ingredients to the butter mixture and mix on low speed just until combined.

Scoop the dough using a #20 scoop (3tbsps / 45 ml) and roll into balls. Roll each ball in graham cracker crumbs and place on the prepared baking sheet, spacing them apart. Use the back of a tablespoon to press an indentation into the center of each dough ball.

Bake for about 9 minutes, until the cookies are soft and just set. While still warm, gently press the centers again to reinforce the indentation. Allow the cookies to cool completely on the baking sheet.

Remove the chilled lime curd from the refrigerator and whisk until smooth. Add the softened cream cheese and whisk until fully combined and creamy.

Spoon the filling into the center of each cooled cookie. Garnish as desired and serve chilled or at room temperature.