Peel the onions and finely slice them. Halve the pepper and scoop out the seeds and white membrane. Slice the pepper into thin strips. Peel and finely grate the garlic and the ginger. Scrub the potatoes and chop into small chunks. Chop the tomatoes into small chunks like the potatoes.
Pour 1 tbsp oil into a large pan and bring to a medium heat. Add the sliced onions and peppers. Sprinkle in a pinch of salt and pepper and fry for 4–5 mins, stirring occasionally, till the veg have slightly softened.
Stir ½ –1 tbsp Goan curry paste into the pan (this spice paste is hot, so add as much or little as preferred) along with the grated garlic and ginger. Continue to cook for a further 1 min.
Tumble the chopped potatoes into the pan along with the tomatoes. Crumble in the coconut cream and vegetable stock cube. Add the peanut butter and swirl in 300ml boiling water. Stir well till combined. Bring to the boil, then cover with a lid and reduce to a simmer. Cook for 25–30 mins, stirring every so often, till the potatoes are tender.
Meanwhile, trim the woody ends and thick stalks from the kale, and shred the tender leaves. When the potatoes are tender, fold the kale into the curry. Continue to cook for 5 mins, till wilted.
Stir the juice from half the lemon into the curry. Taste and add more salt or pepper if you think it needs it. Ladle the curry into warm bowls and serve with wedges of the remaining lemon half on the side for squeezing.