In saucepan set over medium heat, combine milk and caramel syrup; bring to simmer. Meanwhile, in heatproof bowl, whisk egg yolks until frothy.
Gradually whisk 1 cup milk mixture into egg yolks; pour back into saucepan. Cook over low heat, stirring constantly with wooden spoon, for 3 to 5 minutes or until mixture is thickened and coats back of spoon.
In saucepan set over medium heat, combine milk and caramel syrup; bring to simmer. Meanwhile, in heatproof bowl, whisk egg yolks until frothy.
Gradually whisk 1 cup milk mixture into egg yolks; pour back into saucepan. Cook over low heat, stirring constantly with wooden spoon, for 3 to 5 minutes or until mixture is thickened and coats back of spoon.
3. Strain filling through sieve. Pour into six 1/2-cup Mason jars. Cover surface directly with plastic wrap; refrigerate for at least 4 hours or until set. Top each custard with toasted coconut, if desired.