Cut the rump steak into strips. For the marinated method: combine with 3 tablespoons soy sauce and 3 tablespoons rice wine or sherry, then refrigerate for at least 30 minutes. For the spiced method: season with five-spice powder and salt, then coat lightly in cornstarch.
Soak the cloud-ear mushrooms in warm water for 10-15 minutes until softened. Drain and cut into strips.
Heat peanut oil in a wok over high heat. Working in batches to avoid crowding, sear the beef strips for 2-3 minutes until browned. Remove to a plate and set aside.
Add the finely diced garlic and ginger to the wok over medium-high heat and fry for 30 seconds to 1 minute until fragrant.
Add the sliced leek and mushroom strips. Stir-fry for 2-3 minutes.
Return the beef to the wok. Add vegetable broth and rice wine or sherry to deglaze. Bring to a simmer.
Mix 1-2 teaspoons cornstarch with a little pineapple juice from the can to form a slurry. Stir into the sauce and bring to a boil. Simmer for 1-2 minutes until thickened.
Add the pineapple pieces and heat through for 1-2 minutes. Season to taste with sambal oelek and soy sauce.
Serve over fragrant rice or with Chinese noodles prepared by soaking in boiling water for 5 minutes until tender.