Scoop ube halaya jam into eight balls about 2 tbsp or 30g each. Refrigerate while preparing the mochi dough.
In a microwave safe bowl lined with a wet dishcloth (see note), mix shiratamako, sugar, water, and ube extract. Cover and microwave for 2 minutes, or until mochi dough is cooked through.
While still hot, turn out mochi onto a surface dusted with katakuriko. Divide into eight equal parts. Roll or pat each part into a flat circle, roughly 3-4" in diameter.
Take one circle, keeping the rest of the mochi covered with a damp towel to keep it from drying out. Place an ube halaya jam ball in the center, and wrap the mochi around it, pinching the edges to seal into a ball. Roll daifuku in more katakuriko to keep it from sticking.
Repeat with the other seven mochi circles and ube jam balls and serve immediately. Daifuku mochi need to be eaten the day they are made as they dry out quickly.