Adjust oven rack to middle position and preheat the oven to 325 degrees. Line an 8 inch square pan with foil allowing excess to overhang pan sides to allow for easier removal later. Lightly grease foil.

In a food processor, pulse animal crackers into fine crumbs. Add the brown sugar and salt and process until combined (you should have about 1 1/4 cups crumbs). Drizzle butter over crumbs and pulse until crumbs are evenly moistened with butter. Press crumbs evenly and firmly into bottom of prepared pan. Bake until deep golden brown, 18 to 20 minutes.

While crust cooks and cools, in a medium bowl, stir cream cheese, lime zest, and salt with rubber spatula until softened, creamy, and thoroughly combined. Add sweetened condensed milk and whisk until incorporated and there are no lumps of cream cheese. Whisk in the egg yolk. Gently whisk in lime juice until incorporated (mixture will thicken slightly).

Pour the lime filling into crust and spread it to corners with a rubber spatula.

Bake until filling is set and the edges begin to pull away slightly from sides, around 15 to 20 minutes.

Cool on wire rack until they reach room temperature, 1 to 2 hours. Cover pan and refrigerate until completely chilled, at least 2 hours.

Loosen edges with paring knife and lift bars from baking pan using foil hangover.Cut bars into squares and sprinkle with toasted coconut (optional)

Leftovers can be refrigerated for several days- the crust may just soften.