Preheat the oven to 350°F (175°C). Line baking sheets with parchment paper.

In the bowl of a stand mixer fitted with the paddle attachment, cream the butter with granulated sugar and brown sugar on medium until light and fluffy (about 2 minutes). Scrape down the sides as needed.

Beat in the egg and vanilla until combined.

In a large bowl, whisk flour, salt, baking soda, and baking powder. Add 1 cup of the crushed graham crackers (reserve the rest for rolling).

Add dry ingredients to the mixer and beat on low until a cookie dough forms.

Using a cookie scoop (using a 1–1.5 tbsp scoop), portion dough balls; roll each in the reserved graham cracker crumbs. Place on the prepared baking sheets 2 inches apart.

Make an indentation: Using your thumb or the back of a spoon (or the bottom of a 1 tbsp measure), make a well/indentation in the center of each cookie.

Bake the cookies for 10 minutes. Remove from the oven and press the center of each cookie gently with the bottom of a measuring cup to deepen the well; return to bake 2–4 minutes, until the edges are set and centers look dry.

Allow the cookies to cool completely on the sheet, then transfer to a rack. (This helps the filling is set later.)

In a clean bowl, beat cream cheese and sweetened condensed milk until smooth. Mix in key lime juice and lime zest just until combined.

Pipe or spoon the key lime filling into the well in the center of each cooled cookie.

Chill the filled cookies 2 hours (or until filling is set). Top with whipped cream and fresh key lime slices, if desired. Let the cookies come to cool room temp before serving or stored in the fridge until ready.