Place egg yolks in a large bowl; whisk to combine; set bowl aside.
Combine sugar, cornstarch, and salt in a saucepan. Gradually whisk in milk. Cook, stirring, over medium heat until mixture thickens and comes to a boil, 10 to 12 minutes. Remove from heat.
Whisk 1/2 cup hot milk mixture into the reserved egg yolks to temper. Slowly pour warm yolks into the saucepan, stirring constantly. Cook slowly, stirring, over medium-low heat, until mixture begins to bubble, 5 to 6 minutes. Remove from heat. Stir in coconut and vanilla.
Transfer filling to a medium mixing bowl. Lightly butter a piece of plastic wrap, and lay it directly on top of filling to prevent a skin from forming. Chill until firm, at least 1 hour.
This recipe yields the most delicious coconut cream filling EVER. It has such a yummy taste--hard to describe because it's very basic, homey, and "old-fashioned" if that makes any sense...just very rich and comforting, and absolutely perfect with the cake for Coconut Layer Cake. However, this would also be perfect as a pie filling, or on it's own with toasted almonds on top.