Line a tin with plastic wrap.

Place stock, water, butter, salt and rosemary in a large pot. Bring to a simmer then, while stirring with a whisk, pour in polenta in a steady stream. Continue to whisk until mixture is thick. Add parmesan.

Spoon and pat down polenta into tin. Cover polenta and allow to cool completely.

Preheat oven to 200C.

Unwrap polenta and cut into even-sized chips. Line a baking tray with paper. Place chips on to paper and bake for 30 minutes. I don't use oil but you could I guess.