Dulce de leche is a type of condensed milk sweet from Argentina and Uruguay. Traditionally, it is made by heating sweetened cow's milk until it caramelizes and achieves a thick consistency, enough to act as a spread, a filling for cakes and pies, or an ice cream topping.
The legend says that dulce de leche originated in Buenos Aires in 1829, when a maid of Argentinian leader Juan Manuel de Rosas was preparing la lechada by heating sugar and milk. As she left it on the fire a bit longer than usual, she noticed it had become a dark brown substance, and that's how dulce de leche was born.
Other food historians claim it was first created in 1804 by Napoleon's cooks, while others theorize the recipe originated in Indonesia. Either way, it spread through Latin America, and nowadays almost every country in South and Central America has its unique variation.