Preheat the oven to 340 degrees F. Have a clean, ungreased 10-inch tube pan ready.

Whisk the egg yolks with 1 cup of the granulated sugar until pale and thick. Whisk in the oil, pumpkin puree, milk, and vanilla until smooth.

Sift the cake flour, baking powder, salt, and pumpkin pie spice over the wet mixture. Whisk just until no dry streaks remain.

In a clean, grease-free bowl, beat the egg whites with the cream of tartar on medium speed until foamy. Add the remaining ½ cup sugar a little at a time and beat to glossy, medium-stiff peaks.

Fold the meringue into the pumpkin batter in three additions, using a light hand so you keep the air. Stop as soon as it is evenly combined.

Pour the batter into the ungreased tube pan and run a knife once through the batter to pop large bubbles.

Bake for 45 to 50 minutes, until the top springs back and a skewer comes out clean.

Immediately invert the pan and let the cake cool completely upside down. Once cool, run a thin knife around the edges and center tube, then release onto a plate. Dust with powdered sugar before serving.