caramelize
From Longman Dictionary of Contemporary Englishcaramelizecar‧a‧mel‧ize (also caramelise British English) /ˈkærəməlaɪz/ verb 1 [intransitive] if sugar caramelizes, it becomes brown and hard when it is heated2 [transitive] to cook food such as fruit or vegetables with sugar —caramelized adjective caramelized onions→ See Verb tableExamples from the Corpuscaramelize• Cook until onion begins to caramelize.