From Merrian-Webster's Word of the Day:
madeleine \MAD-uh-lun\ nounThe madeleine passage in Proust begins
1 : a small rich shell-shaped cake
*2 : one that evokes a memory
The crack of the bat and the sight of his son running the bases were madeleines for Tom, calling up memories of the great times he had playing the game in his youth.
Did you know?
The madeleine is said to have been named after a 19th-century French cook named Madeleine Paumier, but it was the French author Marcel Proust who immortalized the pastry in his 1913 book Swann's Way, the first volume of his seven-part novel Remembrance of Things Past [À la recherche du temps perdu]. In that work, a taste of tea-soaked cake evokes a surge of memory and nostalgia. As more and more readers chewed on the profound mnemonic power attributed to a mere morsel of cake, the word "madeleine" itself became a designation for anything that evokes a memory.
*Indicates the sense illustrated in the example sentence.
For many years, already, everything about Combray that was not the theater and drama of my bedtime had ceased to exist for me, when one day in winter, as I returned home, my mother, seeing that I was cold, suggested that, contrary to my habit, I have a little tea. I refused at first and then, I do not know why, changed my mind. She sent for one of those squat, plump cakes called petites madeleines that look as though they have been molded in the grooved valve of a scallop shell. And soon, mechanically, oppressed by the gloomy day and the prospect of another sad day to follow, I carried to my lips a spoonful of the tea in which I had let soften a bit of madeleine. But at the very instant when the mouthful of tea mixed with cake crumbs touched my palate, I quivered, attentive to the extraordinary thing that was happening inside me.From Swann's Way, translated by Lydia Davis (New York: Viking, 2002), 45
What was happening? You'll just have to read Swann's Way.
The Way the Cookie Crumbles, Edmund Levin reverse-engineers Proust's madeleine (from Slate)
Other Proust posts, via del.icio.us