Trim the fat from the rump steak and cut into strips. Heat 4 tablespoons oil in a large pan over medium-high heat. Fry the meat in batches for 2–3 minutes per batch, seasoning each batch with salt and freshly grated nutmeg. Remove to a plate.
Peel the shallots and garlic clove. Dice the shallots and press the garlic. In the same pan with the remaining oil, cook the shallots and garlic over medium heat for 2 minutes until softened.
Dissolve 1½ teaspoons cornstarch in 125 ml water until smooth. Pour this mixture and 300 ml coconut milk into the pan. Bring to a boil over medium-high heat, stirring occasionally. Reduce heat to medium-low and simmer for 10 minutes until the sauce thickens slightly.
Return the meat to the sauce and season with salt, 1½ teaspoons sambal oelek, and freshly grated nutmeg to taste. Stir gently and serve immediately.