How to Make It
Oil a 12-by-15-inch rimmed baking sheet. In a saucepan, bring the milk, water and butter to a boil. Add the salt and rosemary. Gradually whisk in the polenta until smooth. Bring to a simmer, whisking, until thickened. Cook over low heat for 15 minutes, stirring. Remove from the heat and let cool for 10 minutes, stirring occasionally.
Whisk the eggs into the polenta, one at a time, then whisk in 1 cup of the Parmesan cheese. Spread the polenta on the prepared baking sheet in an even layer. Let cool to room temperature, then cover with plastic wrap and refrigerate until firm, at least 2 hours or overnight.
Preheat the oven to 400°. Lightly butter a 15-by-10-inch baking dish. Cut the polenta into 2-inch squares. Arrange the squares in the prepared baking dish in a single layer, overlapping them slightly. Pour the cream over the polenta and sprinkle the remaining 1/2 cup of Parmesan on top. Bake for 40 minutes, or until puffed and golden. Let stand for 10 to 15 minutes before serving.