In small saucepan, combine cream, butter, and brown sugar. Cook over medium heat, stirring constantly, until it begins to bubble. Remove from heat, and whisk in vanilla extract.

Pour hot cream mixture over chocolate. Let sit for 5 minutes, and then stir gently until smooth and glossy. Pour into 12 mini tart shells, and allow to cool completely. Cover and refrigerate cooled tarts for 3 hours.

Before serving, decorate with drizzled chocolate, fresh berries, or whipped cream, if desired. Store leftovers in refrigerator in air-tight container.