Heat 1 tbsp of the oil in a large, heavy-bottomed Dutch oven over high heat. Sear the beef in batches, seasoning with some salt and pepper; cook on all sides until browned. Remove the beef to a plate and continue cooking beef and adding more oil as needed. Reduce the heat to medium.
Add remaining oil and the onion and garlic; sauté until almost translucent, about 5 minutes. Add the paprika (or annatto), peanut butter and stir. Whisk the cornstarch or rice flour into the stock and add this all at once to the pan. Whisking to remove any flavourful brown bits from the bottom of pan.
Once the liquid starts to simmer, add back the beef, cover and simmer on medium-low heat for 3 hours, turning the beef over occasionally.
Once the beef yields easily when pierced with a fork, season with fish sauce (if desired), salt & pepper. Skim any fat from the surface of the Kare Kare. Serve over Garlic Rice.

Garlic Rice

Rinse the rice until water runs clear.
In medium saucepan, bring the water to a boil; stir in rice. Cover, reduce the heat to medium-low and cook until the water is fully absorbed, about 12 minutes. Transfer the rice to a bowl to cool slightly.
Heat a large sauté pan over medium-high heat and add the oil and cooked rice. Let the rice crackle and fry, tossing occasionally, until warmed and a little crispy, about 10 minutes. A minute before taking off the heat, add the garlic and green onions and toss. Season to taste.