Place cookies in the bowl of the food processor; pulse until fairly fine, yeilding 1 cup crumbs. Transfer to a medium bowl, and stir in 4 tablespoon melted butter. Press mixture into bottom and sides of 9-inch pie tin. Bake until set and slightly darkened, 12-15 minutes. Do not overbake. Set aside.
Turn oven up to 375°F Fill a small saucepan with water. Add potato; bring to a boil, reduce heat, and simmer until potato is very tender, about 12 minutes. Drain.
In a bowl, combine flour, salt, ginger, cinnamon, nutmeg, and cloves; set aside.
Pass potato through a food mill or potato ricer into the bowl of an electric mixer. Add sugar, eggs and condensed milk. Mix until combined. Stir in remaining 3 tablespoons butter until combined. Add reserved flour mixture, and combine. Pour filling into cooled crust, and bake until filling is set, 30-35 minutes. Serve at room temperature with whipped cream, if desired.