Preheat oven to 325 degrees F.
Sift cake flour and measure, sift all-purpose flour and measure.
Sift both flours together, with baking powder and salt. Gently whisk to aerate more.
Beat butter and sugar together until light and fluffy
Add eggs one at a time, mixing well after each addition.
Add vanilla extract.
Gently fold dry ingredients into the butter and egg mixture in three equal portions, alternating with the evaporated milk. Begin and end with dry ingredients. (Dry-milk-dry-milk-dry)
Pour batter into a well greased and floured 9x13 pan, or two 9 inch cake pans. Tap pans gently to release air bubbles.
Bake approximately 30-40 minutes, or until toothpick comes out with just a few crumbs.
Remove cake from oven and let rest for five minutes in pan, and then gently turn out of pan onto wire rack to cool.