Step 1 The day before serving the final dish, heat the oven to 350 degrees. Generously butter a 9-by-5-inch loaf pan. Line the bottom of the pan with a sheet of parchment paper that has been folded in half to double its thickness and trimmed to fit the bottom of the pan.
Step 2 In a large mixing bowl, beat the eggs, sour cream, milk, Dijon mustard and kosher salt together until homogenous. Add 6 cups of leftover stuffing to this mixture and fold together with a rubber spatula until thoroughly combined.
Step 3Pour the mixture into the loaf pan and gently tap to dislodge any air pockets and to even the surface. Loosely cover the pan with a piece of aluminum foil, taking care not to allow the foil to touch the surface of the food.
Step 4Place in the oven and bake for 1 hour, then remove the aluminum foil covering the pan. Continue to bake until a pairing knife inserted in the center of the loaf comes out clean, about 30 additional minutes. Once done, remove from the oven and set aside to cool on the counter top for about 20 minutes before transferring to a refrigerator overnight.