1½ cups graham cracker crumbs (about ⅔ a sleeve)
2 tablespoons sugar
½ cup sweetened flaked coconut
⅓ cup butter, melted
3 cups sweetened condensed milk (from 3 14-ounce cans)
½ cup sour cream
¾ cup key lime juice
1 tablespoon grated lime zest
Whipped cream and toasted coconut for serving, optional
Heat oven to 350º. Line an 8×8-inch pan with parchment, leaving a few inches overhang on two sides. Butter the parchment and set pan aside.
Combine the graham cracker crumbs, sugar and coconut in a medium bowl. Pour melted butter over and stir to combine. Press mixture into prepared pan and bake for 8-9 minutes. Set on a wire rack to cool.
While crust is cooling, make filling by whisking together the remaining ingredients in a medium bowl. Pour filling into cooled pie crust and return to oven.
Bake for 8-10 minutes, or until the filling feels just firm to the touch. Do not brown. Cool at room temperature, then chill thoroughly. Cut into bars and top with whipped cream and toasted coconut, if desired.