Preheat your oven to 400°F (200°C). Wash and dry 2 medium sweet potatoes, then prick several times with a fork. Place directly on the oven rack and bake for 45-60 minutes until completely tender when pierced with a knife.
Let sweet potatoes cool until comfortable to handle, then remove the skins.
While the potatoes are roasting, prepare your pie crust. If using store-bought, allow it to come to room temperature according to package instructions. Gently press it into a 9-inch pie plate. Crimp the edges decoratively and refrigerate until ready to fill.
Preheat (or reduce) your oven to 350°F (175°C).
In a large mixing bowl, combine the mashed sweet potatoes (you'll need 2 cups) and softened butter, beating until smooth and well incorporated.
Add the sugar to the sweet potato mixture and beat until light and fluffy, about 2-3 minutes.
Add the eggs one at a time, beating well after each addition.
Stir in the evaporated milk, vanilla extract, spices, salt, and bourbon (if using) until the mixture is smooth and uniform.
Pour the filling into the prepared pie crust, smoothing the top with a spatula.
To prevent over-browning, cover the edges of the crust with aluminum foil or a pie shield.
Bake at 350°F for 55-60 minutes, or until the center is almost set but still slightly jiggly.
Remove from the oven and place on a wire rack to cool completely, at least 2 hours. The pie will continue to set as it cools.
Once cooled, refrigerate until ready to serve.
For the optional whipped cream topping, whip heavy cream with confectioners' sugar and vanilla until stiff peaks form. Dollop or pipe onto slices before serving and sprinkle with a dusting of cinnamon.