Soak the dried white beans in plenty of cold water overnight (at least 12 hours). The beans will double in size.

Drain the beans. Place them in a large pot, cover with fresh water, and bring to a boil. Boil for 5 minutes, then drain and rinse the beans. This process, called 'shibunuki', removes astringency.

Return the beans to the pot, cover with plenty of fresh water, and simmer gently over low heat until they are extremely soft and easily crushed between your fingers (about 1.5 to 2 hours). Skim any foam that rises to the top.

Drain the cooked beans. Working in batches, press the warm beans through a fine mesh sieve using a wooden spatula. The skins will remain in the sieve; discard them.

Place the strained bean purée into a clean cotton cloth (sarashi) set over a bowl. Squeeze the cloth tightly to extract as much excess water as possible. You are left with 'naman', raw bean paste.

Transfer the naman to a heavy-bottomed pot. Add the 200g of sugar. Cook over medium-low heat, stirring constantly with a wooden spatula. The mixture will initially loosen, then thicken. Cook until you can draw a line that holds its shape, and the paste forms a stiff peak when dropped. Transfer to a flat tray to cool completely. This is your Shiroan.

Prepare the Gyuhi: In a small microwave-safe bowl, whisk the shiratamako and 30ml water until perfectly smooth. Mix in the 20g sugar. Cover loosely and microwave for 1 minute. Stir vigorously with a wet spatula. Microwave for another 30 seconds until the mixture is translucent, sticky, and stretchy.

Make the Nerikiri Dough: Place 300g of the cooled Shiroan into a non-stick pan over low heat. Add the warm Gyuhi to the pan. Knead them together over the heat using a wooden spatula. Continue to cook and fold until the mixture is thoroughly combined, no longer sticks to your fingers, and feels like soft modeling clay.

Turn the nerikiri dough out onto a clean, lint-free cloth. Using the cloth, gently knead the dough to cool it down, making it exceptionally smooth and pliable. Keep it covered with a damp cloth to prevent drying out.

Divide the nerikiri dough. Reserve a tiny piece (about 5g) and tint it yellow for the flower centers. Tint the majority of the dough a delicate pale pink using food coloring. Knead the color in thoroughly until uniform.

Divide the pink nerikiri into 12 equal portions (about 25g each). Divide the koshian (smooth red bean paste) into 12 equal portions (15g each) and roll them into balls.

Flatten a pink nerikiri portion into a 2-inch disk, thinner at the edges. Place a koshian ball in the center. Gently push the nerikiri up around the filling to encase it completely. Pinch the seam closed and roll into a smooth, slightly flattened dome.

Sculpt the Sakura: Using a sankaku-bera (triangular wooden tool) or the dull back of a butter knife, press 5 equidistant indentations into the sides and top of the dome to divide it into 5 petals. Pinch the outer edge of each petal slightly to form the characteristic cherry blossom notch.

Press a small indentation in the center of the blossom. Using a fine sieve, push the yellow nerikiri through to create 'stamen' threads. Use a bamboo skewer to pick up a tiny cluster of the yellow threads and place it in the center indentation. Repeat for all 12 wagashi.