The practice of layering cakes with sweet substances (honey), intoxicating liquors (wine) and accented with nut flavorings (almonds) was a particular favorite of ancient middle-eastern cooks. The Romans adopted/adapted this recipe and took it with them when they conquered Europe. It is no accident that 16th century English cooks created "trifle." Chocolate and coffee (were introduced to Europe in the 16th-17th centuries but (due to economics) were not incorporated into recipes until the 19th century. According to the the Oxford Companion to Food, Alan Davidson (p. 748) sponge cake was also created in the 19th century. Also related to L’Opera gateau are Genoise (almond-flavored sponge with various decorations and fillings) and Savoy (sponge made by beating egg yolks and whites beaten separately). About "a href="sponge">sponge cake
"Opera gateau is an elaborate almond sponge cake with a coffee and chocolate filling and icing."
—Larousse Gastronomique, completely revised and updated, [Clarkson Potter:2001] (p. 814)
"A classic for the past twenty years, the Opera was created for those who unabashedly choose chocolate and butter cream over fruit desserts. What makes this low, flat cake more modern than any of its predecessors is its shape (usually square or rectangular), and its undecorated sides that show all the layers. L’Opera is traditionally composed of layers of Biscuit Joconde, an almond sponge, that have been thoroughly soaked with coffee syrup…Some pastry shops decorate the top with the word Opera, written in panach with all the swirls that the French love so much…"
—New French Baker, Sheila Linderman [William Morrow:New York] 1998 (p. 66)
"Opera cake. This is a classic chocolate-coffee cake that I believe was first made in the 1930s for an important French-American reception held at the Paris Opera."
—La Nouvelle Patisserie, Jean-Yves Duperret [Viking:New York] 1988 (p. 155)