1.Grease a deep 20cm (8-inch) square cake pan; line base and sides with baking paper.
2.Bring stock to the boil in a medium saucepan; gradually stir in polenta. Reduce heat; cook, stirring, 10 minutes or until polenta thickens. Remove from heat; stir in half the parmesan. Season to taste. Spread polenta in pan. Refrigerate 3 hours or overnight.
3.Preheat oven to 220°C/425°F. Line two oven trays with baking paper.
4.Remove polenta from pan; cut into 20 thick chips. Place chips on a tray; sprinkle with remaining parmesan, turn to coat. Bake 30 minutes or until golden and crisp.
5.Meanwhile, place tomatoes on other tray, drizzle with half the oil; season. Roast in oven for last 7 minutes of polenta chip cooking time.
6.Heat remaining oil in a large frying pan over medium heat; cook prosciutto and rosemary, turning, until prosciutto is golden and crisp. Drain on paper towel.
7.Arrange polenta chips, prosciutto and tomatoes on a platter; top with rosemary and serve with olives.
Polenta can be made to the end of step 2 two days ahead. SERVING SUGGESTION Serve with wood-fired or Italian-style bread.Note