In a stand mixer fitted with a paddle, cream together butter and sugar on medium-low speed until light and fluffy, about 3 minutes. While continuing to mix, stream in lemon juice, followed by milk and vanilla, until evenly combined.
In a bowl, whisk together the flour, cinnamon, ground ginger, nutmeg, grated ginger, cornstarch and salt until combined. With the mixer on medium-low speed, add in one-third of the dry ingredient mixture until combined. Repeat with the next third, then the final third.
Scrape down the sides of the bowl, and transfer dough onto a sheet of plastic wrap. Form the dough into a rectangle no more than ½ inch thick, wrap in the plastic and chill in the refrigerator for at least 1-2 hours.Remove dough from the fridge. Divide in half (this recipe yields two pie crusts, so you can keep one half wrapped in plastic in the fridge). On a lightly floured surface, roll out the dough into a 14-inch round. Transfer to a pie tin, gently pressing down into the corners and up the sides. Trim away excess dough using a paring knife, leaving a 1-inch overhang around the edge. Fold the edges under, then form a fluted edge around the rim with your fingers. Lightly dock the bottom surface of the dough with a fork. Chill or freeze the pie shell in the pie pan until ready to bake.
Preheat the oven to 350°F (180°C).
Line the pie shell with a coffee filter and fill with rice or dried beans to blind bake the crust. Bake in the oven for 14-16 minutes, until the bottom of the pie crust is just lightly baked. Remove from oven and discard the coffee filter and rice/beans. Return the crust to the oven and bake until golden brown, approximately 4 more minutes. Remove from oven and let cool.
To make the pumpkin custard
Preheat the oven to 325°F (160°C).
In a large mixing bowl, combine all ingredients. Blend with an immersion blender until smooth and creamy. (Tip: You’re looking for an even, smooth custard-like filling without any lumps.)
To assemble the pie
Pour the custard into the already-baked and cooled pie crust until just below the top.
Bake for 20-35 minutes (check doneness after 20 minutes; the pie is done baking when a paring knife inserted into the centre of the pie comes out clean).
Let cool on the counter, then chill in the fridge until ready to serve.
Serve with a dollop of fresh whipped cream on top.