Spiced Sweet Potato–Walnut Biscuits

• Walnut Streusel:
• 1/2 cup brown sugar
• 1/2 cup chopped walnuts
• 1/4 cup flour
• 1/4 cup sugar
• 1/4 cup melted butter
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• Sweet Potato Biscuits:
• 2 cups self-rising flour
• 1/4 cup plus 2 tablespoons brown sugar
• 3 tablespoons baking powder
• 1 1/2 teaspoons kosher salt
• 1 teaspoon baking soda
• 1 teaspoon ground cinnamon
• 1/8 teaspoon ground allspice
• 3 tablespoons shortening
• 2 tablespoons butter, cut into 1/2-inch cubes
• 1 cup mashed sweet potatoes (from about 1 large sweet potato, peeled, chopped and boiled until tender)
• 1/4 cup plus 2 tablespoons milk
• 2 egg whites, whisked

Make the walnut streusel: combine the brown sugar, walnuts, flour, and sugar in a bowl. Add the butter and mix well until crumbly. Set aside. 

Preheat the oven to 400ºF.

Make the biscuits: combine the flour, brown sugar, baking powder, salt, baking soda, cinnamon, and allspice in a bowl and mix well. Add the shortening and butter; use a pastry cutter or your hands to break the butter into pea-sized pieces. Set aside. 

In a food processor, combine the mashed sweet potatoes and milk; purée until smooth. Transfer the mixture to the bowl with the flour. Stir just until the dry ingredients are moistened. If the mixture is too dry, add 1 to 2 tablespoons of milk.

Turn out the dough onto a floured surface and knead just a few times. Using your hands, pat the dough into a 1-inch-thick rectangle. Using a 2-inch biscuit cutter, cut out as many biscuits as you can. (You can gather together the scraps and repeat to yield more biscuits, but try to work the dough as little as possible.)

Place the biscuits on a parchment paper–lined baking sheet. Brush with egg white and sprinkle generously with streusel. Bake until the biscuits are nicely browned, about 12 minutes. Serve warm.