The Greek vasilopita, for those more familiar with American cuisine, occupies a ritual place similar to the king cake of cajun tradition. Etymologically they're strangely similar since St. Basil's name means 'king.' It's a light (if prepared well) cake that will
typically be yellow with a glossy brown top. Between us, I'll take a New Orleans king cake over a vasilopita in the taste
Its origins are uncertain, and the stories about it numerous. Perhaps the most plausible (as a story, if not as an actual event) is that the 4th century saint had coins baked into sweet bread made for the poor as a means of giving them the money without it looking like a handout. The recipe and tradition might, for all we know, be as old as money itself but it's become associated with this saint, whose feast is on the 1st of January.
A vasilopita will be, first of all, round. Having only rectangular pans disqualifies you from baking one. Go the nearest confectioner and buy one. Usually it's the first thing to come out after the clock has struck midnight and everyone's done embracing and kissing each other and before everyone pigs out in general and disappears to gamble the night away (that too, "for luck" of course). It's cut into either pie slices or into squares and distributed by the head of the household. When the cake is cut, the two first pieces are dedicated to Christ and to the host's house and finding the coin in either will bring blessings upon the house.
You may not refuse. You can request a small piece but you must eat it. In a less traditional environment you can take a token bite, and spend the rest of the night feeling guilty for not eating it, because that is the right thing to do. Hosts must be prepared to accommodate every guest with a piece--running out of vasilopita before everyone has had a piece is... actually, I don't think I've ever heard of it happening. Running out of food just Does Not Happen at a Greek feast, especially with such a vital item. The surplus vasilopita can be eaten by everyone and, as long as some is left, new visitors will be offered a piece.
In character with the Greeks' love of games of chance, a vasilopita is nothing without some opportunity for monetary gain involved in eating it, and the host is expected not to be stingy with the gift. Before the advent of the euro, larger drachma coins were often substituted for a fixed amount of paper money and the person to find the coin would receive that money. Today a euro coin of a high denomination is acceptable for small-time affairs. Households that can afford to, or really want to show off, will use an English gold sovereign.
Vasilopita is not served exclusively on New Year's Day but is brought out at the first opportunity. Every house, office and organisation needs to have one for the first meeting of the year and, for places like clubs where people gather infrequently, it's actually possible to get an invitation to "cut the pie" as late as March. The average resident of Greece will sample at least a dozen vasilopites before getting really sick of them. Until the next
year, that is.