Preheat oven to 325 degrees Fahrenheit and line the bottom of a 9-inch round cake pan with parchment paper.

Separate the egg whites from the yolks, ensuring no yolk contaminates the whites.

In a large mixing bowl, whisk the egg whites and cream of tartar until soft peaks form, about 2 minutes.

Gradually add 1/2 cup sugar while whisking until stiff, glossy peaks form, about 4 to 5 minutes.

In a separate medium bowl, whisk egg yolks, remaining 1/4 cup sugar, vegetable oil, milk, and vanilla until pale, about 2 minutes.

Sift flour, baking powder, and salt into the yolk mixture and fold gently until just combined.

Fold in one-third of the whipped egg whites to lighten the yolk mixture.

Gently fold in the remaining egg whites in two additions, preserving as much air as possible.

Pour the batter into the prepared pan and smooth the top. Bake for 35 to 40 minutes until golden brown and a cake tester comes out clean.

Remove from oven and let cool in the pan for 10 minutes before turning out onto a wire rack to cool completely.