Part of the Ottoman territories in the Balkans (such as Thessaloniki, Macedonia and Kosovo) were temporarily lost after 1402 but were later recovered by Murad II between the 1430s and 1450s. On 10 November 1444, Murad II defeated the Hungarian, Polish, and Wallachian armies under Władysław III of Poland (also King of Hungary) and John Hunyadi at the Battle of Varna, the final battle of the Crusade of Varna, although Albanians under Skanderbeg continued to resist. Four years later, John Hunyadi prepared another army (of Hungarian and Wallachian forces) to attack the Turks but was again defeated by Murad II at the Second Battle of Kosovo in 1448.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): In what battle did Murad II leave as the victory in 1448?
Second Battle of Kosovo