Step 1

Adjust oven rack to middle position and heat oven to 325 degrees.

Step 2

Cover the bottom and sides of 8 incg pan with a piece of foil. Allowing excess to overhang pan sides. Spray foil with nonstick cooking spray.

Step 3

In a bowl, add sugar to graham cracker crumbs.. Drizzle butter over crumbs and stir until crumbs are evenly moistened with butter.

Step 4

Press crumbs evenly and firmly into bottom of prepared pan. Bake until deep golden brown, 18 to 20 minutes. Cool on wire rack while making filling. Do not turn off oven.

Step 5

While crust cools, in medium bowl, stir cream cheese, zests, and salt with rubber spatula until softened, creamy, and thoroughly combined.

Step 6

Add sweetened condensed milk and stir well until incorporated and no lumps of cream cheese remain; whisk in egg yolk. Add juices and stir gently until incorporated (mixture will thicken slightly).

Step 7

Pour filling into crust; spread to corners and smooth surface with rubber spatula. Bake until set and edges begin to pull away slightly from sides, 15 to 20 minutes. Cool on wire rack to room temperature, 1 to 1 1/2 hours. Cover with foil and refrigerate until thoroughly chilled, at least 2 hours.

Step 8

Loosen edges with paring knife and lift bars from baking pan using foil extensions; cut bars into 16 squares. Sprinkle with toasted coconut, if using, and serve. Let bars stand at room temperature about 15 minutes before serving.)