Preheat the oven to 350°F and generously grease a 9-inch pie pan with butter. Set aside.
Unfurl one sheet of phyllo dough on a clean, dry surface and use a pastry brush to brush with melted butter. Gently fold it in on itself, scrunching into ruffles–almost like making a fan. Gently roll into a loose spiral and place in the center of your prepared pan. If the phyllo dough breaks or tears–don’t worry!
Take the next sheet of phyllo dough and brush with butter, scrunch and gently drape around the spiral in the center, like you were continuing the line. Repeat with the remaining phyllo dough sheets creating a spiral from the outside of the center all the way to the edge. Once the dish is filled, combine the granulated sugar and cinnamon in a small bowl and mix to combine. brush the top with more butter and sprinkle with the cinnamon sugar all over the top.
Bake for 15 minutes or until it is golden brown. It won’t be fully cooked–you’re just parbaking is so it stays crispy after pouring in the custard!
While the phyllo dough is baking, make the custard. In a large mixing bowl, combine the brown sugar, eggs, egg yolk and vanilla extract. Whisk until smooth and combined. Slowly pour in the evaporated milk and whisk together. Add the pumpkin puree, flour, pumpkin pie spice, and salt and mix until smooth.
Pour the custard mixture all over the baked phyllo crust, allowing it to seep into all the layers.
Place the pie back into the oven and bake for 30-35 minutes, or until the custard is set but still jiggles a little in the center.
Let the pie completely before serving. If desired, serve with fresh whipped cream!