Sweet Potato Cobbler

Put flour and 3⁄4 cup of the shortening into a large bowl. Using a pastry cutter or 2 table knives, work shortening into flour until it resembles coarse meal. Whisk together egg, vinegar, and 1 cup ice water in a small bowl; pour into flour mixture. Mix, first with a wooden spoon, then with your hands, into a dough. Form dough into 3 balls, wrap each in plastic wrap, and refrigerate.

Put potatoes, sugar (reserve 1 tbsp. for later use), nutmeg, and 6 cups water into a large pot; bring to a boil over high heat. Reduce heat to medium-low and simmer until potatoes are just tender, 6-7 minutes. Remove from heat.

Preheat oven to 400°. Grease a 9" × 13" × 3" baking pan with remaining shortening. Roll a dough ball out into a 10" × 13" rectangle and cut lengthwise into 3 equal strips. Line only the sides of the pan with dough strips, pressing them together where their edges meet. Bake until crust is a light golden color, about 18 minutes.

Remove pan from oven, fill with half of the potatoes and their water, and dot with 6 tbsp. of the butter. Roll second dough ball out into a 10" × 13" rectangle; drape it over potatoes. Melt 4 tbsp. of the butter and brush dough with half of it. Bake until golden brown, about 20 minutes.

Remove pan from oven, top with the remaining sweet potatoes and their water, and dot with remaining 6 tbsp. of butter. Roll remaining dough ball out into a 10" × 13" rectangle; drape it over potatoes. Brush with remaining melted butter and bake until golden brown, 25-30 minutes. Remove cobbler from oven and sprinkle with reserved sugar and cinnamon. Let cool completely.