FOR THE CRUST
1-1/2 cups finely crushed digestive biscuits
1/3 cup packed light brown sugar
6tbsp unsalted butter, melted
FOR THE FILLING
Two cans milkmaid (condensed milk)
1 cup plain Greek yogurt
1 tablespoon grated lime zest
3/4 cup fresh lime juice
FOR THE TOPPING
1 cup cold whipped cream
1 teaspoon grated lime zest
8 to 10 thin lime slices
Preheat oven to 375 °F and set an oven rack in the middle position.
In a medium bowl, combine the graham cracker crumbs, brown sugar, and melted butter; stir with a fork first, and then your hands until the mixture is well combined. Using your fingers and the bottom of a glass or dry measuring cup, press the crumbs firmly into the bottom and up the sides of a 9 x 1.5-inch pie pan. The crust should be about ¼-inch thick. (Tip: do the sides first.)
Bake for 10 minutes, until just slightly browned. Let the crust cool on a wire rack.
Lower the oven temperature to 350°F.
In a large bowl, whisk together the sweetened condensed milk, yogurt, lime zest, and lime juice. Pour the thick mixture into the warm graham cracker crust. Bake for 15 minutes, until the filling is almost set; it should wobble a bit. Let cool at room temperature for 30 minutes, then place in the refrigerator to chill thoroughly, about 4-5 hours.