Rinse the 200 g azuki beans under cold water, picking out any shriveled beans or debris.

Place the beans in a 3-quart / 2.8 L saucepan, cover with 600 ml water, and bring to a boil over high heat. Boil hard for 2 minutes, then drain in a fine-mesh sieve. This first boil, called shibukiri, pulls out the bitterness azuki beans naturally carry.

Return the beans to the saucepan with 600 ml fresh water. Bring to a gentle simmer over medium-low heat, partially covered, and cook for 60 to 75 minutes, topping up water as needed to keep the beans just submerged, until a bean crushes easily between two fingers with no resistance.

Drain the cooked beans, reserving a splash of the cooking liquid. Return the beans to the pan.

Add the sugar and salt. Cook over medium-low heat, stirring and mashing with a potato masher or wooden spoon, for 12 to 15 minutes, until the mixture thickens to a paste that mounds when you lift the spoon. Add a spoonful of reserved liquid if it looks dry.

Spread the anko onto a plate in a thin layer to cool faster. Cover with plastic wrap pressed directly onto the surface and cool at room temperature for 30 minutes, then chill if not using right away.

Once the anko is fully cool, spoon about 2 tablespoons onto the flat side of one wafer shell.

Top with a second wafer shell, flat side down, and press together gently, just enough to seal. The shells are brittle and crack under too much pressure.

Repeat with the remaining shells and anko to make 6 monaka. Serve right away while the wafer is still crisp.