In a large mixing bowl whisk together the all-purpose flour, Domino® Golden Sugar, and salt.
Using a pastry blender (or two forks), cut in the cold unsalted butter until you have small pea-size pieces. Some larger pea-size pieces are fine too!
Add in the ice-cold water, then using a bench scraper or spatula work it into the pie dough mixture. Rotate the bowl as you scrape the mixture from one side of the bowl to the other until there are no more visible signs of water.
Using your hands, begin to scoop up the dough then press it down with your fingers. Rotate the bowl and repeat, folding the dough until it has formed. Don't forget to include any dry bits of the pieces that may have fallen underneath the dough.
Place the pie dough onto a lightly-floured, clean surface. Pat into a 1″- 1 1/2″ thick disc, then double wrap it tightly in plastic wrap and place in the coldest part of your refrigerator (usually the back) for a minimum of 1 hour. Double wrapping the dough keeps any air from getting in and drying the dough out. The pie dough will keep in the refrigerator for about 2-3 days. If freezing, double wrap and place in a freezer storage bag where it should keep for up to 3 months.
Bring the chunks of sweet potatoes to a boil in a medium saucepan that’s filled with water just covering the sweet potatoes. Reduce the heat to low, then cover and simmer about 15-20 minutes or until sweet potatoes are very tender.
While the sweet potatoes simmer, roll out your prepared, chilled pie crust to about 12-14 inches in diameter.
Carefully place the rolled-out dough into a 9-inch pie plate. Fold the excess pie dough under, then crimp the edges with a fork. Place the prepared pie crust into either the refrigerator or freezer as you work on the sweet potato filling.
Adjust oven rack to 2nd level position (just above center), place a jelly roll pan or baking sheet on the rack, and preheat oven to 425ºF.
Drain the sweet potatoes in a colander, then transfer to a mixing bowl of a stand mixer fitted with a paddle attachment.
Beat the sweet potatoes on medium-high speed until completely mashed and smooth.
Add in the remaining 11 ingredients (the unsalted butter to the salt) and beat on medium-high speed until well blended and smooth.
Pour the sweet potato pie filling into the chilled pie crust, then with a pastry brush, lightly brush the crimped edges of crust with egg wash. You won't use the entire amount of egg wash.
Place the pie on directly top of the heated jelly roll pan or baking sheet in the oven. Bake for 425ºF for 15 minutes.
Keeping the oven door closed, reduce the oven temperature to 350ºF and continue to bake for another 40-45 minutes. At this time, you can choose to add a silicone pie crust shield or a sheet of aluminum foil with a hole cut out to avoid over baking the crust.
Your sweet potato pie will be ready to remove from the oven when there is still some jiggle in the center.
Remove from oven and allow pie to cool and set on a wire cooling rack for at least 2-3 hours. As the pie cools, it will settle. Once cooled, place in the refrigerator to chill.
Decorate with marshmallow meringue, whipped topping, or pipe a cream cheese frosting design onto the top. These are all optional toppings. This brown sugar sweet potato pie is perfect as-is too!
Using a bain-marie or double boiler, heat the egg whites and granulated sugar over 1 – 1.5 inches of simmering water, continually whisking until the sugar has fully dissolved (about 5-6 minutes). You can do a quick test by rubbing a little of the mixture between your pointer finger and thumb to make sure all sugar granules have dissolved.
Transfer the hot mixture to a mixing bowl of a stand mixer fitted with the whisk attachment and set the speed to high. When the mixture initially reaches the soft peaks stage, add in the cream of tartar, salt, and vanilla extract. Continue to mix on high speed right until stiff, glossy peaks form (about 10 minutes).
Top the cooled brown sugar sweet potato pie with the marshmallow meringue topping and, if desired, lightly toast the top using your oven's broiler setting or use a small kitchen blowtorch.
Note there are 2 bake times for this recipe. 15 minutes at 425ºF, then reduce to 350ºF and bake for an additional 40-45 minutes.
The prep time noted above includes prepping and rolling out the pie crust, preparing the sweet potatoes for the filling, making the filling, and assembling the pie. There is also a minimum chill time of 1 hour noted for the pie crust.
To make the egg wash, whisk 1 egg - OR - 1 egg white + 1 tablespoon of water in a small bowl.
Adding the marshmallow meringue topping is an optional step. You can also add dollops of whipped topping, add a decorative cream cheese frosting design, or enjoy as-is!
Keep the sweet potato pie in the refrigerator covered tightly for up to 4-5 days.
To freeze the sweet potato pie, allow it to cool and set completely. Wrap tightly in plastic wrap twice, then cover with aluminum foil. The pie will keep for up to 1 month.