Preheat oven to 400°.
Start by cooking the sweet potatoes. I like to microwave them because it's faster. If you go this route, use a fork to poke several holes into each potato, then place them on a microwave-safe dish and microwave for 6-7 minutes. Use a knife to cut down the center and wait for them to cool down before mashing.
While the sweet potatoes are cooling, make the crust: add flour and sugar to your food processor and pulse. While it's still pulsing, add butter in through the top, then add the water one tablespoon at a time and pulse until everything's combined. A big ball of dough should form.
Flour a flat surface, then roll the dough out into a circle, approximately ¼" thick, and carefully transfer it into your pie pan. Trim the edges then crimp them to your liking; set aside. You'll most likely have some extra dough both from rolling it out and trimming and that's ok!
Scrape out the sweet potato and discard the skin, placing the sweet potato directly into a bowl and using a fork or potato masher to mash it. Then, measure it out to make sure you have 2 cups of it. Add mashed sweet potato, milk, sugar, syrup, vanilla, cinnamon, nutmeg, and salt to your blender, then pulse for 1 full minute until smooth.
Pour filling into pie pan, using the back of a spoon to smooth it out.
Bake pie for 15 minutes at 400°, then reduce heat to 350° and bake for an additional 35-45 minutes. The center will still be jiggly once it's "done" and that's ok -- it'll firm up completely once it cools.
Remove pie from the oven and transfer it to a cooling rack. Let the pie cool for 30-60 minutes at room temperature, then transfer it to refrigerator so it can cool completely. Enjoy cool (like pumpkin pie), or warm it back up before serving.