In a medium-sized bowl, mix pecans with Swerve, egg white, salt & vanilla until combined. Press firmly into the bottom and a little up the sides of 9" springform pan.
Cream the cream cheese, pumpkin puree, Swerve, eggs, egg yolks, sour cream, pumpkin pie spice, lemon zest, and vanilla in the bowl of an electric stand mixer fitted with a paddle attachment (or use a handheld mixer) on medium-high speed until completely smooth.
Pour into nut crust. Smooth top with a spatula.
Place a pan of hot water in the bottom of the oven to keep the cake from cracking. Don't skip this step or your gorgeous cheesecake will crack right across the top.
Bake at 4ooº for 20 minutes. The cheesecake will turn golden and puff. Reduce heat to 275ºF and bake 1 hour & 20 minutes longer, or until it is set on the edges but it may still be a little jiggly in the center when you gently shake the pan. This is okay, it will set as it cools.
Take the cake out of the oven and allow it to come to room temperature for another 2 to 3 hours or until completely cooled. Cheesecake will deflate. Leave the cheesecake in the springform pan, wrap tightly with plastic wrap and refrigerate overnight.** Do not skip this step! Cheesecake must be allowed to chill at least 8 hours for the flavors and texture to come together.
When you're ready to eat the cake remove it from the refrigerator and let it sit for at least 10 minutes. To release it from the springform pan, run a hot knife around the outside of the cake. Leave the cake on the bottom of the springform pan for serving.
Cut into 12 slices. Optional: serve with whipped cream.