Place the butter, garlic, thyme, basil and salt into a medium bowl. Mix well.
Heat a cast iron skillet over medium heat. Spread the butter mixture on the bread slices. Place 2 bread slices, butter-side down, into the skillet. Top with the cheese and remaining bread slices, butter-side up. Cook until the sandwiches are lightly browned on both sides and the cheese is melted.
Heat the soup according to the package directions. Cut the grilled cheese sandwiches into squares and serve on top of the soup.