Haw flakes were once and will always be a favorite snack of mine. I went to elementary school in San Francisco's Richmond district, which is one of the several unofficial Chinatowns we have around here, and Haw Flakes were an unquestioned part of every black-haired child's snack life.
The ingredients are simple: haw, sugar, water. The discs recall communion wafers and melt away if you place them on your tongue and wait patiently. Press them to the roof of your mouth, and they break apart softly into grainy pieces that dissolve quickly. The taste is only very slightly tart and mostly fruity, but again in a kind of oblique manner, not so exaggeratedly flavored in the camp way of mainstream American fruit snacks. Some have compared it to the taste of fruit leather or fruit roll-ups, which I think is more or less accurate, despite the difference of texture.
It turns out that "haw" in fact refers to the crushed up berries of the hawthorn tree and used to be eaten in rural areas of the American south before the industrial food system taught people to be afraid of food that didn't come from a grocery store (though the Chinese hawthorn may vary from trees found in this hemisphere).
Here is a great description of Haw Flakes on Asiangrocery.com that was written as a serious information source after the site had to take down its earlier reference to a Haw Flake writeup by some "totally clueless American" when said "clueless American" wrote Asiangrocery.com to complain and threaten a code-yellow Homeland security alert. Read angry letter here. And click here to read the angry American's original post, which includes such choice lines as, "What's a firework doing with an ingredient list? And what the hell was a 'HAW', anyway? Haw haw haw! Well, since the whole ten-pack cost thirty-nine cents, I figured what the hey." and "There was no way I was going to eat these babies until I figured out what 'haw' meant - I didn't want to find out it was Chinese for 'pig innards' after knocking down a pack."