Position the oven rack in the bottom third of the oven, and preheat to 400 ° F.
Pierce the sweet potatoes with a fork several times. Cook in microwave on high until tender, about 4-6 minutes per side. Microwave times will vary.
Cut the cooked sweet potatoes open, and cool completely. Scrape the potato flesh into a bowl, and mash it with a potato masher or a sturdy fork until smooth. Measure the potato puree to equal 1 ½ cups.
Place the 1 ½ cups of puree in a large bowl, and mix in the brown sugar until well combined. Whisk in the remaining pie filling ingredients, whipping cream through salt, until just combined, don’t overbeat.
Brush the crust with beaten egg white. Transfer the filling to the crust.
Bake pie until filling is puffed around the edges and just set in the center, about 45 minutes. Transfer to a rack to cool.
Notes
Pie can be made 1 day ahead. Cover and refrigerate.