Tiramisu is an Italian layered desert consisting of Savoiardi cookies (biscuits to the British, or "lady fingers" colloquially—slightly dry small sponge cake wafers) dipped (or soaked but not to saturation) in very strong coffee (espresso, traditionally) then layered with a very light custard made of Zabiglione (egg yolks, sugar and sweet wine (traditionally Marsala) or a liquor as a flavoring) and Mascarpone (a very rich, slightly sweet and slightly stiff Italian cream cheese). The carefully dipped-in-expresso cookies are then layered with the custard, then sprinkled with cocoa, and refrigerated.

The word tirami-su quite literally means "pick me up"; this makes sense if you think about the effects of the coffee, and the liquor. I'm not even going to attempt to unravel the history of Tiramisu as a dessert though; it's far too complicated, and too likely to cause headaches; I'd much rather eat it. I will note the following:

There are a number of very similar layered Italian desserts involving Savoiardi, custard bases, coffee and liquor flavorings. Some of these are several hundred years old, and there seems to be several "local" traditions of such a dessert. I've seen completely plausible explanations for why Tiramisu is a traditional dessert of Venice, or Treviso, and of Sienna. There are also similar desserts in other cooking traditions; I have described Tiramisu, more than once, as caffeinated trifle. The name Tiramisu to refer to an Italian dessert is verifiably several hundred years old, and there does seem to be a close association in Italian cuisine with coffee and liquor flavored layered desserts being deemed appropriate for women whose health is perceived as delicate, and with a dessert associated with cafes attached to various historic high-profile Italian brothels in the late nineteenth and early twentieth century. If you're curious, and willing to risk the headache, I suggest looking here, and here, though I note that in addition to numerous histories of Italian cuisine, there is at least one book just on the history of Tiramisu.

It does seem clear that, no matter by what vector, Tiramisu became popular as an elegant and luscious dessert in America during the 1980s, first in San Francisco, and then it spread very very rapidly. It's now very much, like crème brûlée, one of the most likely desserts to find on any restaurant's dessert menu. I note, though I shall refrain from judgement, that I have seen Tiramisu flavored coffee, a Tiramisu martini, and Tiramisu ice cream. The ice cream was lovely. The coffee scared me, and I'm considering the martini; it used Starbucks' coffee liquor, Godivia Chocolate liquor, and Bailey's with vodka; having written that, I have to admit that it too scares me. The dessert form of Tiramisu, however, is still very much on my list of things to order.

The key ingredients of the Tiramisu layers are the Savoiardi, and the filling that goes between the layers. The filling is made of Zabiglione, and Mascarpone, and flavored, traditionally with Marsala. You may sometimes see the combination of Zabiglione and Mascarpone referred to Mascarpone creme. The Mascarpone is easy to find at most grocery stores in the cheese section. You will likely have to go to a wine or liquor specialty store to find Marsala; it's a fortified wine that comes in a range of styles from dry to semi-cry, to sweet; you'll want the sweet version. Most recipes for Tiramisu include a sub-section on actually making Zabiglione, though they often do not actually indicate that that is what you are doing. If you have a personal favorite recipe for Zabiglione, then by all means feel free to substitute it. I would be cautious, however, about any recipe that does not call for beating the egg yolks over a bowl of water brought to a boil then reduced to a simmer; using raw eggs can lead to salmonella.

Savoiardi are a variant of lady fingers closely associated with the Piedmont region of Italy. They are quite easy to make, and you can likely find lady fingers at the local grocery, or at your favorite bakery. I use the word variant because quite honestly, Savoiardi are not identical to lady fingers. They are not, typically, quite as soft or as sweet as ladyfingers. It's worth actually making a batch of Savoiardi the day before you plan to make and assemble the Tiramisu. There's a good recipe here. It's not the end of the world if you're short of time and decide to buy lady fingers at the store instead, however.

You will need to decide ahead of time whether you plan to assemble the Tiramisu layers in a single serving dish or individual dishes. The single dish looks lovely, but can be difficult to serve; the individual servings can be time consuming to assemble. Though the basic ingredients of Tiramisu are very much standardized, there are an infinite number of variations, particularly in terms of the flavorings used, the espresso, the presence or absence of the Marsala, or the substitution of another liquor, are all likely to vary.

My personal pick for a basic Tiramisu recipe is this one from the Pioneer Woman's cooking blog. It's one of the best cooking sites, ever, and here are her illustrated step-by-step instructions for Tiramisu. This site is just about Tiramisu, with more variants and recipes than you could possibly want. Michael Chu of Cooking for Engineers has a step-by-step illustrated recipe for classic Tiramisu. Chu offers precise but easy to follow instructions. Emeril Lagasse has a Tiramisu version that uses home made sponge cake and Grand Marnier; he also makes a version with rum.