2 pounds whole sweet potatoes, washed and patted dry 1 9-inch pie crust 1 cup evaporated milk 1/4 cup melted unsalted butter, cooled 3 large free-range eggs, yolks and whites separated 1/2 cup brown sugar, packed 1/4 cup granulated sugar 2 teaspoons pure vanilla extract 1 teaspoon ground ginger 1 teaspoon ground cinnamon 1/4 teaspoon ground nutmeg 2 pinches ground Himalayan pink salt 1/2 teaspoon lemon zest whipped cream, for serving