First, boil the potatoes in their skins, peel them off and dice them. Dice the onion and garlic and then sauté in the oil. Add the tomato paste and stir well. Deglaze with the broth and bring to the boil.
Stir in the frozen beans and simmer over medium heat for about 15 minutes. The cooking time depends on personal taste (I prefer vegetables that are firm to the bite). Finally season the dish with salt, pepper and harissa and fold in the potato cubes to heat, do not boil any more.