Preheat oven to 375°F. Lightly grease a 9x13-inch baking pan with cooking spray.
In a large mixing bowl, beat the shortening and sugar till very light, about 2-3 minutes.
2/3 cup shortening, 1 3/4 cup granulated sugar
Beat in eggs one at a time, and then add the vanilla extract.
2 large eggs, 1 1/2 teaspoons pure vanilla extract
In a separate bowl, whisk together the flour, baking powder and salt. Add the dry ingredients alternately with milk, mixing in about 1/2 the flour mixture on low speed just until mostly incorporated, then adding half the milk and mixing well to combine, then repeating with the remaining flour mixture and milk. Stop the mixer to scrape the bottom and sides of the bowl once or twice during the process and do not overmix.
2 1/2 cups all-purpose flour, 2 1/2 teaspoons baking powder, 1/2 teaspoon salt, 1 1/4 cups whole milk
Spread the batter into the prepared baking pan and bake for 30-35 minutes, making sure to check the cake with a toothpick for doneness. It should come out mostly clean with just a few crumbs sticking to it. Be careful not to overbake the cake.