Preheat your oven to 350°F (175°C). Lightly spray a 9-inch pie plate with non-stick cooking spray.
If using whole graham crackers, process them in a food processor or crush in a sealed bag with a rolling pin until finely ground. In a medium bowl, combine the graham cracker crumbs, sugar, and cinnamon (if using).
Add melted butter to the crumb mixture and mix until it resembles wet sand. Every crumb should be moistened.
Press the crumb mixture firmly into the bottom and up the sides of your pie plate. Use the bottom of a measuring cup to compress the crumbs for a more stable crust.
Bake the empty crust for 8 minutes. Remove from oven and let cool slightly while preparing the filling. Keep oven at 350°F.
In a large bowl, whisk together the pumpkin puree and sugar until well combined.
Add eggs one at a time, whisking well after each addition. Stir in vanilla extract, pumpkin pie spice, and salt until fully incorporated.
Gradually add the evaporated milk while stirring continuously. Mix until the filling is smooth and uniform in color, with no streaks remaining.
Carefully pour the pumpkin mixture into the pre-baked graham cracker crust, leaving about ¼ inch of space at the top.
Bake at 350°F for 45-50 minutes. The pie is done when the center is almost set but still slightly jiggly—like firm gelatin. The edges should be set while the very center should have a slight wobble.
Allow the pie to cool completely on a wire rack at room temperature (at least 2 hours). For best results and easiest slicing, refrigerate for at least 4 hours or overnight.