Place a piece of pineapple on the end of each skewer. Preheat an indoor or outdoor grill to medium-high. While the grill is heating, make the sauce by placing the butter and brown sugar in a small pot set over medium heat, stirring occasionally, until both are melted and well-combined. Stir in whipping cream. Bring to a boil, stirring occasionally. Remove from heat and stir in vanilla. When the grill is hot, lightly oil the surface and grill the pineapple skewers 1 to 2 minute per side. Divide and arrange the skewers among four plates. Drizzle the skewers with the caramel sauce and serve each portion, if desired, with a scoop of vanilla ice cream.