Soak: Place 150g of purple rice in a bowl and cover with plenty of cold water. Let it soak at room temperature for at least 8 hours, or overnight.

Cook: The next day, drain and rinse the rice. Transfer it to a rice cooker or pot, add 300ml of fresh water, and cook until tender and all water is absorbed (use the "white rice" setting on a rice cooker).

Season: While the rice is still hot, immediately add 30g of sugar and the packet of sweetened condensed milk (if using). Stir vigorously until everything is well combined and the mixture is sticky.

Shape: Let the mixture cool until it's easy to handle. Then, portion and roll it into balls, each weighing about 30g. Set them aside on a plate.

Mix Dry Ingredients: In a large mixing bowl, combine 100g whole wheat flour, 200g all-purpose flour, 3g yeast, and 10g sugar. Whisk together.

Add Liquid: Make a well in the center and gradually pour in 160g of warm water. Use chopsticks or a fork to stir until a shaggy dough forms with no dry flour remaining.

Add Fat & Knead: Add the spoonful of lard (or oil) to the bowl. Use your hands to work it into the dough initially, then turn the dough out onto a clean, un-floured surface. Knead vigorously for about 10 minutes until the dough is very smooth, elastic, and no longer sticky.

Portion: Shape the dough into a log and cut it into equal pieces, each weighing about 40g. Cover them with a damp cloth to prevent drying.

Shape Wrappers: Take one piece of dough and use a rolling pin to flatten it into a round disc, about 3-4 inches in diameter. The center should be slightly thicker than the edges to prevent the bun from bursting when steaming.

Fill and Seal: Place one 30g purple rice ball in the center. Gather the edges of the dough around the filling, pleating as you go (like wrapping a baozi). Pinch the top firmly to seal completely.

Final Shape: Place the bun seam-side down on the counter. Gently cup your hands around it and rotate to form a neat, round shape. If desired, lightly press the bun with a round mold to create a decorative pattern.

Prepare Steamer: Line your steamer baskets with parchment paper.

Final Proof: Place the shaped buns in the steamer, leaving about 2 inches of space between them as they will expand. Cover with the lid and let them proof in a warm, draft-free place for 30-40 minutes. They are ready when they look puffy and feel light; a gentle poke will leave a slight indentation that slowly springs back.

Steam: Bring the water in your steamer to a rolling boil over high heat. Once boiling, place the proofed buns (in their baskets) on top. Steam on medium-high heat for 12 minutes.

Rest: Crucial Step: After 12 minutes, turn off the heat. DO NOT OPEN THE LID. Let the buns sit in the steamer with the lid on for an additional 5 minutes to gradually adjust to the temperature. This prevents them from collapsing.