Grease a 6cm deep, 19cm square cake tin. Line base and sides with baking paper, extending paper 2 cm from edge of pan on all sides. Place stock, rosemary and garlic in a medium saucepan over high heat. Bring to boil. Reduce heat to low.
Add polenta in a slow steady stream, stirring constantly. Cook, stirring for 5 minutes or until thickened. Stir in parmesan. Spread polenta into prepared pan. Cover. Refrigerate for 3 hours or until set.
Preheat oven to 220 degrees Celsius Remove polenta from pan. Cut in half. Cut each half into 2cm wide chips. Place on a greased wire rack over a baking paper lined baking tray. Spray with oil. Bake 15 minutes or until golden and crisp.
Note: Chips can be frozen, unbaked, for up to one month.