Tip the potato sachets into a large heatproof bowl and mix in 300ml boiling water. Add a pinch of salt and lots of black pepper, then mix in the egg and flour. Knead briefly into a soft pliable dough. Divide into 4.
Using your hands, lightly roll each piece of dough on a lightly floured surface to make a sausage as wide as your thumb. Use a sharp knife to cut into 3cm pieces. Transfer to a lightly floured tray to keep them separate and prevent them sticking.
Preheat the oven to gas 7, 220°C, fan 200°C. Bring a pan of water to the boil. Add the gnocchi in 3 batches, cook for 1-2 mins (or until they rise to the top), then remove with a slotted spoon. Transfer to a large, shallow baking dish.
Meanwhile, tip the pasta sauce into a pan and gently bring to the boil. Stir in the cherry tomatoes, olives and some black pepper.
Spoon the sauce over the gnocchi and tear over the mozzarella. Mix the breadcrumbs with the oil; sprinkle over the gnocchi. Bake for 15 mins.
Garnish with basil and serve with salad, if you like.
