Preheat a pan on one side of the griddle to medium heat. Melt butter in the pan on low heat and whisk in flour until combined. Cook for 1 minute, whisking constantly, until the flour is fragrant. Gradually whisk in chicken stock, followed by milk, stirring until smooth. Let cook for about 10 minutes, stirring frequently, until thickened.
Season the gravy with SPG seasoning and poultry seasoning.
On the opposite side of the griddle, preheat to medium heat and add a dab of butter with a bit of neutral oil. Sauté onions for 2 minutes, then add turkey. Chop the turkey if needed and cook until heated through. Transfer turkey to the gravy and mix in frozen peas. Let cook for 5 more minutes.
Toast sourdough bread on both sides in butter or mayo spread, ensuring a golden-brown finish.
Serve the turkey gravy over the toasted bread as an open-faced sandwich or in a bowl. Garnish with fresh sage if desired.
Pro Tip: This dish can also be served over mashed potatoes, biscuits, or dinner rolls. Add any leftover Thanksgiving vegetables for extra flavor!
