To avoid a mouthful of grit, molluscs like clams should be purged. To do this, simply put them in a large bowl of cool water and leave for 30-40 minutes. Once purged, give them a rinse and they are ready to cook.
Put the water and kombu in a large pan and bring to the boil. Remove the kombu and add the salt and polenta, stirring continuously. When the polenta starts to splutter, turn the heat to low and simmer, stirring occasionally, for 40 minutes or until cooked (polenta is cooked when it pulls away from the sides of the pan). Remove from the heat, spread thinly over a flat baking sheet and leave to cool.
Mix the garlic with the olive oil in a bowl and heat the grill (broiler) to hot. Once the polenta is cool, cut into 8 squares and brush the surface of each with the garlic oil. Place under the hot grill for 10 minutes, until it starts to become crispy and golden. Turn and cook the other side until golden.
Heat the tomato sauce in a large pan and, once hot, add the clams, stirring them through the sauce. Cover and cook over a high heat for 6 minutes or until the clams have opened.
Serve with the polenta and Italian green salad.