My colleague Jason Rudkin-Binks (our trade marks expert) has said this:
Trade mark infringement can only occur where a word / phrase / logo is used “as a trade mark”, i.e. where it is used as a brand to denote trade origin. It is not trade mark infringement to use a term in a descriptive manner. The use you describe sounds like descriptive use, i.e. you are using “dulce de leche” in accordance with its accepted meaning to describe the sweet sauce that is known by that name. Your use is also on the back of pack. You are in effect using it to describe an ingredient. Note, we haven’t looked at whether DOLCE can be used as a brand as that involves conducting a formal clearance search.
We hope that helps and good luck with your ice cream product!