NOTE: Season as desired with salt and pepper at each stage. But season lightly: dish should be undersalted, since it will be eaten with salty bagoong.
Place the onion and oxtail in a large pot. Add water to cover. Bring to the boil. Reduce heat and simmer for 2.5 to 3 hours or until tender. (Or cook for 35 minutes in the pressure cooker at high pressure.).
When preparing the banana blossom and eggplant, as you slice, put the pieces into water with a bit of lemon juice, to prevent them turning brown.
Heat a big skillet or wok and add vegetable oil. Saute the garlic. Add the eggplant, banana blossom, and long beans; cook for 10 minutes. Add baby bok choy and cook for 5 minutes more, until vegetables are crisp-tender. Reserve vegetables.
Remove meat from broth, keeping broth in pot. If desired, when cool enough to handle, remove meat from bones. Add meat to vegetable mixture; reserve.
Add a little broth to the peanut butter; stir until well blended, adding more broth if necessary. Bring the broth to a simmer. In a bowl, combine annatto powder with cold water; mix until smooth; add annatto mixture to broth. Simmer, stirring, until sauce thickens and does not taste floury.
Add meat and vegetables, and cook until heated through. Meat should be very tender; vegetables should be tender but not falling apart. If desired, add water to make more sauce.
Serve with bagoong (fermented shrimp paste). I prefer the guisado (sauteed) kind, regular flavor (not sweet or hot).
* NOTE * Fresh banana blossom should be large and dense, and feel tightly packed. * To clean: First take off the outer dark red bracts and accompanying tiny matchsticks (baby bananas!) -- these are inedible. Continue until you reach the pale pink/yellow inside and it's becoming difficult to peel apart. Cut off the inedible stem. Cut blossom into 1-inch slices, dropping into lemon water to prevent browning. Separate the blossoms (like you would leeks). If possible, let them soak for a little while, to remove any bitterness. * You can use the same water for the eggplant. *.