The Milky Way
(1940) This short is based on the nursery rhyme about the three little kittens who lost their mittens. Their mother sends them to their rooms without dinner. From their room, they see the Milky Way and sail up to it, using a basket and helium balloons, passing through some fanciful astronomical bodies, until they reach a Milky Way filled with every conceivable form of milk, including milkweed and Milk of Magnesia.
Walt Disney won the Oscar for Short Subject (Cartoons) for the first eight years it was awarded (1932-39); this classic cartoon broke his streak and is clearly one of the best cartoons of the era.