The word bubur tells you this is a rice porridge, but while most bubur dishes are savory, this one is sweet. The porridge, which has a pudding-like consistency, is topped with palm sugar syrup.
According to The Food of Indonesia, "Bubur Sumsum is the Indonesian equivalent of a Jewish mother's chicken soup: if you have a problem, eat a bowl of Bubur Sumsum and all will be well."
This version, which I got from at the Benhill traditional market, certainly meets the definition of a comfort food: blandly sweet, not too complicated, and easy to eat even if you have a toothache or a sore throat. The porridge was a bit salty and the syrup quite sweet, with a slightly caramelized flavor. If I were designing my own, I'd use more bubur and less syrup, because I found this version very sugary.
I've never made Bubur Sumsum, but the recipe looks pretty easy. The surprise ingredient is chalk. According to the recipe, Indonesian cooks say it adds a "gentle, soft flavor."
Look for rice flour and palm sugar at Asian grocery stores, and chalk at an office supply store (or have a child pilfer some from school). You could substitute brown sugar for the palm sugar, but it won't be as flavorful.
1.5 cups rice flour
6 cups water
1 teaspoon powdered white writing chalk
1/2 teaspoon salt
Palm sugar syrup (simmer equal parts palm sugar and water together for ten minutes; strain)
Mix first three ingredients and strain through a fine sieve. Bring to a boil in a heavy pan. Simmer for about 30 minutes until thick. Cool to room temperature, top with coconut mixed with salt, and pour palm sugar syrup over.