In a small bowl, combine the water and sour cream; set aside.

In a large mixing bowl, stir the flour, sugar and salt together. Scatter the shortening over the flour, then use a cheese grater to grate the butter on top. Using a fork or a pastry blender, cut the mixture together until it resembles coarse crumbs. Add the sour cream mixture and use a stiff rubber spatula to stir and press the dough together until it forms one big mound. If dough is still too dry and doesn’t hold together, add another tablespoon of water.

Turn the dough onto a piece of plastic wrap and flatten into a 5-inch disk. Wrap tightly and refrigerate for at least one hour.

Once chilled, roll the dough out into a 12-inch circle and fit into a greased 9-inch pie plate. Trim, fold, and crimp the edge of the dough. Place in the freezer for 15 minutes until chilled and firm.

Preheat the oven to 400ºF. To blind-bake, I like to press a sheet of aluminum foil into the pie pan since it gets into the crevices better than parchment paper. I then pour two cups of granulated sugar on top of the foil, and use a spoon to press the sugar down into the foil. Place pie plate onto a baking sheet and bake until the edges of the crust are starting to brown, about 15-16 minutes. Remove pie from the oven and carefully lift the aluminum foil (with the sugar) out of the pie. Return the pie crust to the oven and bake until the bottom crust is golden brown, about 14-15 minutes longer. Remove and cool completely.

In a medium saucepan over medium heat, stir together the brown sugar, heavy cream and butter until the sugar dissolves and the mixture comes to a full boil, about 5 minutes. Remove from the heat, and stir in the vanilla and salt.

Reserve 1/4 cup of the milk. Slowly add the remaining milk to the sugar mixture.

In a medium bowl, whisk together the 1/4 cup of milk, cornstarch, and egg yolks, until combined. Slowly pour the cornstarch mixture into the sugar mixture over medium-low heat and cook, stirring constantly, until thick, about 3-5 minutes.

Strain the filling through a fine mesh sieve set over a bowl. Pour the filling into the prebaked pie crust. Place pie uncovered in the refrigerator for 1 hour before covering with plastic wrap and allowing to chill in the refrigerator for at least 6 hours, preferably overnight.

Once pie is set, whip the heavy cream with the powdered sugar in a stand mixer fitted with the whisk attachment until stiff peaks form. Spread whipped cream on top of pie. Top with butterscotch curls, if desired.