Hearty Swiss Potato Casserole

Ingredients (13)

• + ¼ cup butter add to pantry
• + ¼ cup whole wheat flour add to pantry
• + 1 ⅔ cups water, divided add to pantry
• + 1 ½ teaspoons cornstarch add to pantry
• + 1 pinch salt and ground black pepper to taste add to pantry
• ✓ 1 pinch salt and ground black pepper to taste
• + ½ teaspoon ground thyme add to pantry
• ✓ ½ teaspoon dried rosemary
• + ¾ cup shredded Swiss cheese add to pantry
• + ¾ cup shredded Swiss Gruyere cheese add to pantry
• + 3 medium potatoes, peeled and thinly sliced add to pantry
• + 2 scallions, finely chopped add to pantry
• ✓ 1 clove garlic, minced