ROSE’S heavenly CAKES: Caramelized Pineapple Pudding Cakes (page 342) suggests to refrigerate the completed pudding cakes for 12 hours, still in the pan.  also to reheat over hot water.

http://www.realbakingwithrose.com/2010/12/caramelized_pineapple_pudding.html

this provides the maximum release of caramel sauce and prevents a hard caramel top as this picture:

i have also tested that microwaving for 3 minutes, then rest for 5 minutes, does the same trick.