Blue and Gold Souffle

Name: Blue and Gold Souffle
Ingredients: 3 cups leftover mashed potatoes - made with Yukon Gold potatoes; 2 scallions, white and light green parts, chopped; 1 egg; 1/3 cup milk; 3 ounces blue cheese, crumbled, divided; 2 slices bread (preferably sourdough or italian); 1/4 cup fresh parsley; 1 butter, cut into small cubes; 1 tablespoon extra blue cheese for topping