Brioche and Grape Bread Pudding

6 cups Brioche, challah, or egg bread, cut into 3/4 inch cubes

1 cup red California seedless grapes

3 eggs, large

1 egg yolk

1 teaspoon vanilla extract

6 tablespoons packed light brown sugar

3 cups heavy cream

Brown Sugar Whipped Cream (optional):

1 tablespoon packed light brown sugar

1 cup heavy cream

1 teaspoon vanilla extract