This is a savory side dish with the added crunchy sweetness of the grapes.
In a large saucepan, melt butter over medium heat. Add onion; season with salt and pepper, and cook, stirring occasionally, until tender, 3 to 5 minutes. Add rice and rosemary; cook, stirring, about 1 minute.
Add broth and 1 cup water; bring to a boil over high heat. Reduce to medium-low heat; cover, and cook until liquid is absorbed and rice is tender, 20 to 25 minutes.
Add grapes and parsley; season with salt and pepper, and stir to combine.
Make pilaf up to one day ahead, adding grapes and parsley after reheating.