1. Preheat oven to 350°F. Spread coconut in an even layer on a rimmed baking sheet. Bake, stirring once or twice, until golden, 8 to 10 minutes. Let cool completely. Leave oven on.
2. Process cookies and 1/2 cup coconut in a food processor until finely ground and mixture begins to clump together, about 2 minutes.
3. Transfer mixture to a 9-by-13-inch rimmed baking sheet; press into an even layer on bottom. Bake until golden and firm to the touch, 12 to 15 minutes. Let cool on sheet on a wire rack.
4. Whisk together the granulated sugar, cornstarch, and salt in a large saucepan. Whisk in milk and egg yolks.
5. Cook over medium heat, whisking constantly, until mixture comes to a boil, 5 to 6 minutes. Continue to cook, whisking constantly, until thickened, about 3 minutes more.
6. Remove from heat. Add butter, whisking until combined. Stir in 1 1/2 cups coconut.
7. Spoon the custard onto cooled crust; smooth top with an offset spatula. Press plastic wrap directly onto custard surface, to prevent a skin from forming. Refrigerate until set, about 3 hours.
8. Beat cream and confectioners' sugar in a large chilled stainless-steel bowl until stiff peaks form. Set aside.
9. Cut custard-filled crust into 24 bars (each about 3 by 1 1/2 inches). Transfer to a platter. Spoon whipped cream into a pastry bag fitted with a medium star tip. Beginning at one corner, pipe a zigzag pattern over each bar. Sprinkle bars with remaining 1/2 cup coconut.

Makes 2 dozen.