Dulce de Leche can be brought into the US if it is in a checked in luggage.
I saw an Argentinian woman go into second inspection at the US Customs in Atlanta and had her visa (I believe she had an H1) revoked for bringing in fake Louis V. bags. (the purse she was carrying, the sunglasses and the satchels) US Customs is cracking down on people who buy fake designer bags, etc.
Let this not happen to you. It was embarrasing.
Dulce de Leche, just declare if the US Customs asks you...did you bring anything to eat?