Bring milk, sugar, salt, and 2 tablespoons butter to a simmer in a large saucepan, stirring until sugar and salt have dissolved and butter has melted. Remove from heat, and let cool to 110 degrees.
Meanwhile, sprinkle yeast over warm water in a small bowl, and let stand until foamy, about 5 minutes. Stir into milk mixture. Add 5 cups flour, and stir until a stiff dough forms (if dough is too sticky, add more flour, 1/4 cup at a time).
Turn out dough on a lightly floured work surface, and knead until smooth. Transfer to a large buttered bowl, cover with a clean kitchen towel, and let rise in a warm, draft-free place until doubled in size, about 2 hours.
Divide dough into 24 pieces. Roll each piece into a smooth ball. Space 2 inches apart on buttered baking sheets, and cover each with a towel. Let rise until doubled in size, 45 minutes to 1 hour.
Preheat oven to 400 degrees. Melt remaining 2 tablespoons butter, and lightly brush on top of rolls. Decorate with rosemary if desired. Bake until golden brown, 10 to 15 minutes. Let cool on sheets on wire racks. Rolls can be stored in an airtight container for up to 2 days.