Special equipment: one 8 1/2-by-4 1/2-by-2 1/2-inch glass loaf pan
Preheat the oven to 375 degrees F; generously grease the loaf pan with butter.
Whisk together the flour, sugar, beer, rosemary and Parmesan in a large bowl until evenly incorporated yet slightly lumpy. Transfer to the prepared loaf pan. Bake until golden and a skewer inserted into the center comes out clean, 45 minutes. Unmold onto a rack and let cool. Cut into 1-inch slices and serve with butter.