c.1230, from O.N.
kaka "cake," from W.Gmc.
*kokon-, from PIE base
*gag-, *gog- "something round, lump of something." Not related to L.
coquere "to cook," as formerly supposed. Replaced its O.E. cognate,
coecel. Originally (until c.1420) "a flat, round loaf of bread."
Caked "thickly encrusted" (with) is from 1922.
Let them eat cake is from Rousseau's "Confessions," in reference to an incident c.1740, when it was already proverbial, long before Marie Antoinette. The "cake" in question was not a confection, but a poor man's food.
"What man, I trow ye raue, Wolde ye bothe eate your cake and haue your cake?" ["The Proverbs & Epigrams of John Heywood," 1562]