Preheat grill or grill pan over medium-high heat.
Combine melted butter, brown sugar and cardamom. Brush mixture on cut side of pluots. Grill cut side down for 2 minutes or until caramelized, turn and grill an additional 1-2 minutes, until softened.
In a small bowl, microwave white chocolate and 2 tablespoons heavy cream on high for 20 seconds, stir until smooth. In the bowl of an electric mixer beat remaining ¾ cup heavy cream and vanilla at medium speed, gradually adding white chocolate until soft peaks form. Serve with pluot halves and garnish with white chocolate curls if desired.