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You can do it with coarse bean paste or with こしあん. In the first case, it's more common to have grilled 切り餅, in the second case prepare little dumplings (MR25).
In either case, serve this with something salty, like 大徳寺なっと or salted sea weed. For this, either find a small plate, or use a 信玄弁当箱.
Recipes
Serving
KS23 said that あわぜんさい is more common, which is cooked milled mixed with little 餅 pieces and with a drop of liquefied あん. I didn't think it looked particularly great; and while she argues it's more traditional for CNY, I think I prefer the soup.