Step 1

Place the sweet potatoes in a large pan and add enough cold water to cover the potatoes by about an inch.  Bring to a boil, salt the water, and cook until tender, about 15 minutes.  Drain, then add the potatoes back to the pot.

Step 2

Meanwhile, preheat the oven to 425ºF.

Step 3

In a large skillet or Dutch oven, heat the olive oil over medium-high heat.  Add the turkey and cook, breaking it up with your spoon.  When the turkey is almost cooked through, add the onion, carrots, celery and poultry seasoning.  Season with salt and pepper, and cook until the vegetables start to soften, about 5 minutes.

Step 4

In a saucepan, melt 4 tablespoons of the butter.  Whisk in the flour, and allow to cook for a minute.  Slowly add the chicken broth, whisking the whole time to avoid clumps.  Season with salt and pepper and the Worcestershire sauce.  Simmer for a few minutes until thickened.  Stir in the frozen peas, then remove from the heat and stir into the turkey mixture.

Step 5

Add the remaining tablespoon of butter and the sour cream to the cooked sweet potatoes.  Season with salt and pepper and mash until the potatoes are free of lumps.

Step 6

Pour the turkey mixture into a 9×13-inch baking dish.  Top with the mashed sweet potatoes and smooth the top.  Sprinkle the cheese over the top.  Bake until the cheese is completely melted, about 5 minutes.

Step 7

Let sit for 5-10 minutes before serving.