In a large bowl, combine 1 cup gruyere cheese, 3 tablespoons sour cream, 2 teaspoons Dijon mustard, 1 teaspoon Worcestershire sauce and 1 tablespoon chopped chives to form a smooth paste. Spread the paste over 4 slices thick white bread. Top each with 1 slice smoked ham and another slice thick white bread to form a sandwich. Butter the outsides of each sandwich. Heat a non-stick frying pan over medium heat, place the sandwiches in the pan and cook for 3-4 minutes on each side until golden brown and crisp.