Bring the milky water to the boil in a pan. Stir in the salt, cornmeal and herbs, reduce the heat and simmer for approx. 10 mins. over a low heat, stirring constantly to form a thick paste. Rinse a baking tray in cold water and spread the polenta onto the back of the tray (approx. 28 x 36 cm). Leave the polenta to cool, cut into slices measuring approx. 4 x 8 cm.
Mix the crème fraîche, olives and tomatoes, season.
Spread both sides of the polenta slices with oil, cover and grill over/on a medium heat (approx. 200 °C for approx. 5 mins. on each side. Serve the polenta slices with the dip.