INGREDIENTS

Filling:

12 ounce sweet potato, peeled and cut into 1/2-inch dice

1 tablespoon olive oil

2 tablespoons unsalted butter

1/2 cup diced onion

1/2 cup diced celery

1/2 cup diced carrot

1 teaspoon chopped fresh thyme

1/3 cup dry white wine

1/4 cup unbleached all-purpose flour

2 1/2 cups low sodium chicken broth

2 cups diced cooked turkey

1/2 cup frozen peas

3/4 teaspoon salt

1/4 teaspoon ground black pepper

Biscuit topping:

3/4 cup + 2 tablespoons unbleached all-purpose flour

1/2 teaspoon baking powder

1/4 teaspoon baking soda

1/4 teaspoon salt

4 tablespoons cold unsalted butter, cut into small pieces

1/2 cup buttermilk

1 egg yolk, lightly beaten

DIRECTIONS

1. Preheat the oven to 425°F. 

2. For the filling, combine the sweet potatoes and oil in a bowl and toss to coat. Arrange potatoes in a single layer on a nonstick 11 x 17-inch cookie sheet. Roast until tender and just starting to brown, about 15 minutes. Remove from the oven and cool. 

3. Meanwhile melt the butter in a large nonstick skillet over medium heat. Add the onion, celery, carrot and thyme; cook, stirring occasionally, until starting to soften, 2-3 minutes. Pour in the wine, bring to a boil and cook until almost completely evaporated, 3-3 1/2 minutes. Sprinkle the flour over the vegetables and cook, stirring, 1 minute. Stir in the broth, bring to a boil and cook until thickened, 1-2 minutes. Remove from the heat and stir in the reserved sweet potatoes, turkey, peas, salt and pepper. Transfer mixture to an oval 2-quart au gratin baking dish. 

4. For the biscuit topping, combine the flour, baking powder, baking soda and salt in a bowl. Add the butter and using a pastry blender cut the butter into the flour until the mixture looks like coarse crumbs. Stir in the buttermilk until the flour is just moistened; knead the dough 2-3 times in the bowl to bring it together. Turn the dough out onto a lightly floured surface and roll out to 1/4-inch thickness. With a 2 3/4-inch round biscuit cutter, cut out 10 biscuits, rerolling scraps as needed, and set them on top of the turkey filling. Brush the tops with the egg yolk. 

5. Bake until the biscuits are golden and the filling is bubbly, about 18-20 minutes. Let cool 10 minutes before serving.