Preheat the oven to 375°. In a small bowl, mix the first 4 ingredients. In a large bowl, whisk the eggs. Whisk in the pumpkin, evaporated milk, and the sugar-and-spice mixture; pour into the piecrust.
In a medium bowl, mix cream cheese, egg yolk, sugar, and lemon zest plus juice until smooth. Dollop small spoonfuls onto the top of the unbaked pie and, using a skewer or the tip of a knife, swirl into the pumpkin filling.
Bake until just set in the center, about 1 hour; let cool completely on a wire rack. Serve with whipped cream, if using.
