Set oven to 350 degrees Fahrenheit (175 degrees C). A 9x13-inch baking dish should be greased and floured.
Flour and baking powder should be combined in a small bowl. Place aside.
Butter and sugar should be creamed till light and fluffy in a large bowl. Stir in vanilla after beating in the eggs one at a time. Add the flour mixture gradually and stir just until combined. Batter should be poured into the dish.
A toothpick placed into the center of the cake should come out clean after 30 to 40 minutes of baking in a preheated oven.
In the meantime, combine whole milk, evaporated milk, and sweetened condensed milk in a medium bowl.
Notes
If you want a richer cake, you can use heavy cream in place of the whole milk.