01 - In a large bowl, whisk together sweetened condensed milk, Greek yogurt, key lime juice, lime zest, vanilla extract, and a pinch of salt until fully blended.
02 - With an electric mixer or whisk, whip the cold heavy cream in a separate chilled bowl until stiff peaks form. Gently fold the whipped cream into the lime mixture until smooth and homogenized.
03 - Line a 9x9-inch pan with parchment paper. Pour in the lime ice cream mixture, smoothing the top evenly. Freeze for at least 4 hours or until solid.
04 - Set oven temperature to 350°F (175°C) and line a baking sheet with parchment paper.
05 - In a bowl, combine graham cracker crumbs, all-purpose flour, baking powder, and salt.
06 - In a separate bowl, beat unsalted butter and brown sugar until light and fluffy. Add the egg and vanilla extract, and continue mixing until incorporated.
07 - Gradually add dry ingredients to the butter mixture, mixing just until fully combined; avoid over-mixing.
08 - Scoop 16 tablespoon-sized balls of dough onto the prepared baking sheet, flatten each slightly. Bake for 8 to 10 minutes until golden at the edges. Allow cookies to cool completely.
09 - Once frozen, remove the ice cream slab from the pan and use a round cookie cutter matching the cookies' size to cut out ice cream rounds.
10 - Place one ice cream disc between two cooled graham cracker cookies, pressing gently to adhere. Serve immediately or wrap each sandwich and freeze until ready to enjoy.