01 - In a large mixing bowl, whisk together sweetened condensed milk, Greek yogurt, key lime juice, key lime zest, vanilla extract, and salt until smooth.
02 - In a chilled bowl, whip the heavy cream using an electric mixer until stiff peaks form. Gently fold the whipped cream into the lime mixture until fully incorporated and smooth.
03 - Line a 9x9-inch pan with parchment paper, pour in the key lime ice cream mixture, smooth the surface, and freeze for at least 4 hours until firm.
04 - Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.
05 - In a medium bowl, combine graham cracker crumbs, all-purpose flour, baking powder, and salt.
06 - Beat together the unsalted butter and brown sugar in a separate bowl until light and fluffy. Add the egg and vanilla extract, beating to incorporate.
07 - Gradually blend the dry ingredients into the wet ingredients, stirring just until combined.
08 - Scoop 16 tablespoon-sized portions of dough onto the prepared baking sheet, flatten each slightly, and bake for 8-10 minutes until golden. Allow cookies to cool completely.
09 - Once the ice cream is firm, use a round cookie cutter matching the cookie size to cut out discs.
10 - Sandwich each ice cream disc between two graham cracker cookies. Serve at once or wrap tightly and return to the freezer until ready to serve.