Bring a large pan to a medium-high heat. Pour 1 tbsp coriander seeds into the dry pan and fry for 2 mins, shaking occasionally, till toasted and fragrant. Tip into a mortar and pestle and crush well. No mortar and pestle? Tip the seeds into a sturdy bowl and bash with the end of a rolling pin or jam jar to crush.
Finely chop the fresh coriander stalks (set the leaves aside for later). Peel and grate the garlic cloves and add both ingredients to the mortar and pestle. Sprinkle in a generous pinch of salt and pepper and grind into a rough paste.
Peel and finely slice the onions. Trim and halve the pointed pepper, and flick out the seeds and membrane. Finely slice it into thin strips. Peel the sweet potatoes and cut into bitesize chunks.
Pour 1 tbsp oil into the large pan and return to a medium heat. Slide in the onions and the garlic and coriander paste. Sprinkle in a little cayenne (it’s very hot, so use as much or little as you prefer). Fry for 5 mins, stirring occasionally, till softened. Add the pepper slices and mix well. Continue to cook for a further 5 mins.
Tip in the sweet potatoes and pour in the chopped tomatoes, along with 1 tbsp peanut butter and 250ml boiling water. Bring to the boil, then cover with a lid, reduce to a simmer and cook gently for 25 mins, or till the sweet potatoes are tender when pierced with the tip of a knife.
While the mafe simmers, pour the couscous into a bowl and add 300ml boiling water. Cover the bowl with a large plate or chopping board and set aside to soak for 15 mins, then fluff up with a fork.
Heap the couscous into 2 bowls and spoon over the peanut mafe. Finish with a sprinkle of the reserved coriander leaves and a small pinch of cayenne to serve.