This recipe is adaptable to any relatively thick caramel filling.
Dulce de leche would work, and some folks fill these with peanut butter. (See links, below.) Don’t melt down chocolate chips, which are formulated to hold their shape when heated, and you’ll find the chocolate too sludgy to work with.
Depending on the size of the cups, and how generous you are, you may get a few more, or a few less, than indicated.