Peel the pears and cut them in 1/2 through the stem end. Use a melon baller to scoop out the cores. Put the pear halves in a large bowl. Sprinkle over the vanilla; toss. Then sprinkle over the brown sugar, flour, cinnamon, and nutmeg and toss to coat the pears with the flavorings. Line the pears up in a buttered, sugared baking dish, rounded sides up.
In the same bowl, mash together the butter, brown sugar, flour, and salt with your hands for the topping. Toss in the cranberries. Crumble the topping mixture over the pears in the baking dish and bake until the topping is crunchy and browned and the pears are very tender, 35 to 40 minutes. Serve with whipped cream.