Preheat Panini press while assembling Panini. Mix chocolate-hazelnut spread milk and thyme in bowl until well blended and smooth. Brush one side of each bread slice lightly with butter. Place half of the bread slices buttered side down on a clean work surface. Divide plum and Brie slices evenly among bread slices. Drizzle lightly with chocolate-hazelnut sauce. Top each with a second slice of bread buttered side up. Place 2 sandwiches at a time on Panini press and close. Cook 2-4 minutes or until bread is golden brown with grill marks and cheese is melted. Remove to wire rack to cool slightly before cutting.
