01 - In a large mixing bowl, combine sweetened condensed milk, Greek yogurt, key lime juice, key lime zest, vanilla extract, and a pinch of salt. Whisk until the mixture is fully incorporated.
02 - In a separate chilled bowl, whip cold heavy cream using an electric mixer until stiff peaks form. Gently fold the whipped cream into the lime mixture, ensuring a smooth, uniform texture.
03 - Line a 9x9-inch pan with parchment paper. Pour in the prepared ice cream base and smooth the surface. Freeze for a minimum of 4 hours, until fully set.
04 - Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper.
05 - In a mixing bowl, whisk together 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 egg and vanilla extract, mixing until thoroughly combined.
07 - Gradually add the dry ingredients to the butter mixture. Stir until just combined, being careful not to overmix.
08 - Portion the dough into 16 equal tablespoon-sized balls. Arrange on the prepared baking sheet, flattening slightly. Bake for 8 to 10 minutes, or until golden brown. Cool cookies completely on a wire rack.
09 - Once the ice cream is firm, use a round cookie cutter matching the cookie size to cut out discs of ice cream. Sandwich each disc between two graham cracker cookies.
10 - Serve ice cream sandwiches immediately or wrap each individually and return to the freezer until ready to enjoy.