Make the graham cracker cookie dough: In a large bowl, add the butter, sugars, and salt. Beat with a rubber spatula (or a hand mixer) until light and fluffy. Stir in the eggs and vanilla until combined. Add graham crackers to a large Ziplock bag, seal, and bash them with a rolling pin to make small crumbs. Add the graham cracker crumbs and flour to the cookie dough. Mix until evenly incorporated and set in the refrigerator to chill while you make the filling.

Make the key lime filling: Meanwhile, in a medium bowl mix the sweetened condensed milk, Greek yogurt, lime juice, lime zest, flour, and salt. Set in the refrigerator to chill while you preheat the oven.

Bake the cookies: Preheat oven to 350F with a rack in the lowest position. Line a half-sheet tray with parchment paper. Using a quarter-cup ice cream scoop, plop 8 graham cracker cookie dough balls evenly spaced on the tray. Using your thumb, make a thumbprint into the center of each dough ball, using more of your fingertips to make the cavity larger (the larger the cavity, the more filling it’ll hold, just make sure there’s enough of a “wall” around the cavity). Fill the holes with the key lime filling. Bake for 13-14 minutes, until the filling is set and the edges of the cookies begin to pick up some color. Allow the cookies to cool completely on the tray. Transfer cookies to a sealable container and allow to chill in the refrigerator. Repeat this process with remaining dough and filling.