Begin by bringing 4 cups of water to a rolling boil in a sturdy Dutch oven or large soup pot. Add the sirloin steak tips, crushed garlic cloves, and ground ginger, stirring everything together. Reduce the heat to maintain a gentle simmer, cover the pot, and allow it to cook for 20 minutes, stirring occasionally. Don't worry if you notice any foamy scum forming on top; you can simply skim it off with a spoon or stir it back into the brew. Once the initial simmer is complete, remove the pot from heat and carefully drain the beef, reserving the flavorful cooking liquid to use later. Return the same pot to medium heat and pour in 2 tablespoons of cooking oil. When the oil shimmers and shows it’s hot, add the chopped red onions and sauté them, stirring now and then, until they turn soft and translucent—this usually takes about 5 to 7 minutes. Next, introduce the chopped tomatoes to the softened onions. Cook this mixture, stirring occasionally, until the tomatoes break down and meld nicely with the onions, approximately 3 to 5 minutes. Add the drained beef back into this tomato and onion base, stirring well to coat the meat in the rich mixture. Let it cook on medium heat for about 5 minutes, stirring occasionally to integrate the flavors. Now, it's time to add the key spices: sprinkle in the paprika, black pepper, curry powder, and the tomato puree, along with a dash of salt to suit your taste. Stir thoroughly to combine all the ingredients evenly. Pour the reserved beef cooking water back into the pot, and add just enough additional water so the beef mixture is fully covered. Bring it all up to a boil, then reduce the heat to low and let it simmer uncovered. Stir occasionally and let it cook for about 1 hour, or until the beef is tender and the sauce has thickened beautifully. If you notice the curry starting to stick or dry out, add a splash more water to maintain a pleasant consistency—whether you prefer it thick or a bit soupy. When your Kenyan beef curry is cooked to perfection, remove it from the heat. Taste and adjust the seasoning as you prefer. For a vibrant finishing touch, garnish with freshly sliced chili and a handful of fragrant cilantro leaves. This final flourish adds a lovely burst of color and a hint of fresh heat to each serving. Tip: For even more flavor depth, marinate the beef in the garlic and ginger with a pinch of salt for an hour before cooking. Serve with fluffy steamed rice or warm flatbreads to soak up the luscious curry sauce.