01 - In a large mixing bowl, whisk together sweetened condensed milk, Greek yogurt, key lime juice, lime zest, vanilla extract, and a pinch of salt until smooth.
02 - In a chilled bowl, whip the cold heavy cream to stiff peaks. Gently fold the whipped cream into the lime mixture until evenly 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 or until fully set.
04 - Preheat the oven to 350°F. Line a baking sheet with parchment paper.
05 - In a medium bowl, combine graham cracker crumbs, all-purpose flour, baking powder, and salt.
06 - In a separate large bowl, beat the unsalted butter and brown sugar together until light and fluffy. Beat in the egg and vanilla extract until well blended.
07 - Gradually stir the dry ingredients into the butter mixture, mixing just until a dough forms. Avoid over-mixing.
08 - Scoop 16 tablespoon-sized balls of dough onto the prepared baking sheet. Gently flatten each. Bake for 8 to 10 minutes until golden brown. Cool cookies on a wire rack.
09 - Once frozen, remove ice cream from the pan. Using a round cookie cutter matching the cookie size, cut out 8 discs of ice cream.
10 - Place one ice cream disc between two graham cracker cookies, pressing gently to adhere. Serve immediately or wrap sandwiches and store in the freezer until ready to enjoy.