Preheat oven to 350°F. Generously grease a 10- to 12-cup Bundt pan with baking spray that contains flour, or coat it with butter and flour.
In a large bowl, whisk together the flour, sugar, baking powder, pumpkin pie spice, and salt.
In a separate bowl, whisk together the pumpkin, milk, eggs, melted butter, and vanilla until smooth.
Pour the wet ingredients into the dry ingredients. Stir just until combined, being careful not to overmix.
Pour the batter into the prepared Bundt pan.
Bake for 50 to 65 minutes, or until a toothpick inserted into the thickest part of the cake comes out with a few moist crumbs but no wet batter. Start checking at 50 minutes.
Let the cake cool in the pan for 10 to 15 minutes, then carefully invert it onto a wire rack.
While the cake is still warm, brush the melted butter evenly over the surface.
In a small bowl, mix the sugar and pumpkin pie spice. Sprinkle the mixture over the warm cake, gently pressing it onto the surface and rotating the cake as needed for an even coating.
Let the cake cool completely before slicing.