Place a grill pan over low heat. Lay the panettone on a work surface and cut each in half diagonally to make 6 triangles. Using a pastry brush, liberally brush each side of the panettone with the melted butter. Place the panettone triangles on the grill for 30 to 45 seconds until crisp and toasted. Transfer the triangles to 6 serving plates. Place 1 scoop of ice cream on top of each triangle. Garnish with the slivered almonds and serve immediately.