Montreal-style Smoked Meat
Papalo, a leafy herb, has a distinctive flavor that I've heard compared to mint, cilantro, and laundry detergent. There's no good substitute. Mexican expats have been known to smuggle mass amounts of papalo seeds through American customs to be able to grow it (and eat it) at home in the States. Nowadays you can find papalo at many Mexican grocery stores.
The ingredients: roast pork, ham, Swiss cheese, sliced pickles and mustard on crusty Cuban bread, all toasted in a sandwich press called a plancha. Traditionalists frown upon versions that include ingredients like salami, mayonnaise, lettuce, and tomato.
Read more: Cuban Medianoche recipe
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Bacon Butty / Rasher Sandwich
Read more: Bacon Butty recipe
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Croque Monsieur / Croque Madame
Read more: Dinner Tonight: Pan Bagnat
Smorrebrod / Butterbrot
Germany's butterbrot is similar enough to warrant inclusion here. It's also an open-faced sandwich made on buttered bread. In Germany, the preferred bread is sourdough and the most popular topping is wurst, which can mean sliced sausages or cold cuts. A butterbrot with wurst is known as a wurstbrot, while a butterbrot with eggs is an eierbrot, with cheese a kosebrot, and so on.
Tea Sandwich (a.k.a. Finger Sandwich)
Pork Belly Bun
Rou Jia Mo
Read more: Vada Pav, the Indian 'Burger'