Preheat grill for medium heat and lightly oil the grate.
Heat 6 tablespoons butter, white sugar, and nutmeg in a saucepan over medium heat, stirring until sugar is dissolved, about 5 minutes. Brush pineapple spears with butter mixture.
Arrange pineapple on preheated grill and cover; grill until lightly browned, turning occasionally, 7 to 10 minutes. Transfer pineapple to a platter.
Melt remaining 1/2 cup butter in another saucepan over medium heat. Stir in brown sugar and heavy cream. Bring to a boil, stirring constantly. Remove from heat and add vanilla extract and salt. Serve pineapple topped with cream sauce and ice cream.