For the squash: Preheat the oven to 375 degrees F.
Put the squash on a sheet tray, toss lightly with olive oil and toss in the oven. Roast the squash until a fork slides in and out easily, about 45 minutes. Remove the squash from the oven and let cool. Remove the skin and puree until smooth. Place 3 cups squash puree in a large mixing bowl, reserve the rest for another purpose.
For the crust: In the bowl of a food processor combine all the flour, sugar, cinnamon, allspice, ginger, nutmeg and salt. Toss in the butter and pulse until the mixture looks like grated parmigiano. Add in the egg yolk and a few drops of the ice water. Pulse until the mixture starts to come together into a ball. Add a few more drops of water if the mixture still seems dry.
Turn the dough out onto a lightly floured work board. Using the heels of your hand, schmear the dough straight forward and roll it back with your fingertips. Repeat this process two more times. Form the dough into a disk, wrap in plastic and refrigerate for at least 1 hour.
Remove the dough from the fridge and let warm up for 5 minutes. Roll the dough out into a large circle and lay in a deep pie dish. Trim the dough all the way around so there is only 1/2-inch overhang. Fold the dough under and crimp the edges decoratively. Make sure the edges don't extend beyond the pie plate rim. Prick the dough all over with a fork. Lay aluminum foil over the dough to cover and fill the pie plate with baking beans.
Place the pie plate on a sheet tray and bake in the oven for 15 minutes. Remove the foil and baking beans and bake for 5 more minutes. Remove from the oven and let cool.
Reduce the heat in the oven to 350 degrees F.
For the filling: In a small bowl, beat the eggs until they are smooth. Beat in the cream. Add the cream/egg mixture to the squash puree and beat to combine. Beat in the condensed milk, brown sugar, bourbon if using and vanilla. Beat until the mixture is well combined, 1 to 2 minutes.
Pour the squash mixture into the prepared pie shell. Place on the sheet tray and place back into the oven for 25 minutes. Rotate the pie and bake until the mixture barely jiggles when shaken, another 20 to 25 minutes. If the crust starts to get too dark, place a pie shield ring on the pie to protect the edges from burning.
Remove the pie from the oven and let it cool for at least 1 hour before cutting.
Whip heavy cream with a pinch of cinnamon until stiff peaks, and top the pie as a garnish.