Cover oxtail and beef short ribs with water in the slow cooker. Cook on low for eight hours.
Soak annatto seeds in warm water for about 10 minutes.
Sautee shallots and garlic in a pan.
Whisk in cooking broth, ground peanuts, annatto-infused water, sugar, and fish sauce.
Add oxtail and beef shortribs. Bring to a simmer.
Add in vegetables to cook.
Season with more fish sauce or salt if needed.
Serve with rice and shrimp paste on the side.