MARLBOROUGH — The shop that Madrid-born Sergio Mendoza and his wife, Lia, opened three years ago and turned into Madrid European Bakery & Patisserie had been another bakery. The couple went about replacing sheet cakes and other American-style baked goods with beautiful European cakes, petit cream puffs and eclairs, and simpler treats, such as butter cookies, coconut macaroons, and butterfly-shaped puff pastry palmiers. On weekends, Mendoza, the sole pastry chef, makes croissants and other morning pastries.

One of Mendoza’s more modest cakes is getting the bakery attention. He makes tarta de Santiago, an almond torte that is one of Spain’s most popular confections. Rich, moist, and almost slightly chewy — the texture is somewhere between a tender cake and a macaroon — the tarta is a butterless, flourless batter of ground almonds, eggs, sugar, and citrus rind.

While almond cakes are ubiquitous in Spain, tarta de Santiago is of particular renown in the northwest region of Galicia. It’s named for St. James, whose relics are believed to be buried in the grand cathedral of Santiago de Compostela. The cake is often dusted with confectioners’ sugar and marked with the image of the ornate cross of St. James. According to Mendoza, there are official guidelines regulating the ingredients and proportions for a cake to be called tarta de Santiago. “My recipe conforms to that,” he says. But he, like most Spaniards, is not sure of the recipe’s origins.

Cookbook author Claudia Roden, in her thoroughly researched 2011 tome, “The Food of Spain,” writes about the cake’s probable history. She believes tarta de Santiago was originally a flourless Passover cake from Andalusia, in the south of Spain. From her home in London, Roden explains in an e-mail: “I had a theory about the tarta de Santiago because almonds do not grow and never did grow in Galicia, nor do lemons or oranges, and because it is exactly like many almond cakes made by Sephardi Jews who came from countries like Syria, Turkey, and Italy. It is well known that the Jews had an important presence here when they fled the south . . . in the 12th century and later.”

Continue reading below

Most pastry chefs in Spain have their own version. Mendoza tweaked another baker’s recipe to come up with his, which he adapts for different nuts, such as pistachio and hazelnut. Others include pistachio-almond, coconut-almond, hazelnut with fine chocolate chunks, and a new lemon poppy seed. Last year he introduced a pumpkin-almond cake. “It was a big hit,” he says, but he took it off the menu in March so customers wouldn’t grow tired of the flavor. He intends to bring it back in the fall. Tartas sell for $19.95 to $23.95 (slices from $2.95 to $3.45).

In Spain, he says, tartas are often cheapened by the use of wheat flour, with only minimal (and more expensive) ground almonds in the batter. Mendoza’s cakes are flourless (they are gluten-free), with just finely ground blanched almonds. Batches of almond meal can be subtly different — drier, finer, or coarser — so it takes a good eye, he says, to know exactly how the batter should look. “Not too liquid or too thick,” he says.

Mendoza, 36, started baking when he was 9. In his parents’ bakery business, he loved working with doughs for brioche, croissants, and bread. “It’s the first thing you start touching,” he says. He later moved on to creams, mousses, and frostings, and honed his craft while still in his teens. “The masters teach you why you do and don’t do certain things,” he says of his many teachers.

When his parents sold the bakery and moved to Florida in 2003, Mendoza followed a year later. He met Lia in Orlando and the two moved to Connecticut and later to Massachusetts. Mendoza worked mostly in supermarket bakeries, including Whole Foods Market in Newtonville. It was a dream for the couple to open their own shop. It sits next door to the Wayside Country Store, a building that dates to 1790.

Today, the bakery is supplying some independent shops with tartas and shipping them to Hawaii, California, and Puerto Rico.

Two years ago, Lia gave birth to a son. The tartas are so much a part of the couple’s livelihood that you can probably guess what they named him. It’s quite a popular name throughout Spain: Santiago.

Madrid European Bakery & Patisserie 1019 Boston Post Road, Marlborough, 508-485-8844, www.madridbakery.com. Almond tartas are also available at Wasik’s Cheese Shop,

61 Central St., Wellesley, 781-237-0916.