Madagascan bean stew

INGREDIENTS

200 g

(~ 7 oz) baby new potatoes

1 tbsp

oil

1/2

onion, (finely diced)

400 g

tin black beans, (drained but not rinsed (240g, or ~ 1 1/4 cups, when drained))

400 g

tin kidney beans, (drained but not rinsed (240g, or ~ 1 1/4 cups, when drained))

3 cloves

garlic, (minced)

1 tbsp

pureed ginger

large tomatoes, (chopped)

1 tbsp

tomato puree

Salt

Black pepper

250 milliliters

(~ 1 cup) vegetable stock

1/2 tbsp

cornstarch

1 tbsp

water

large handful rocket ((arugula))

Cooked rice, (to serve (optional))