Sift together the flour, sugar, baking powder, and salt.
Add the palm shortening or cold butter cubes and rub them into the flour mixture until the entire mixture looks like fine crumbs.
Store the dry cake mixture in an airtight container for up to 6 months if you used palm shortening, or for up to two weeks if you used butter (mix made with butter may also be stored in the freezer to extend its shelf life to six months).
To make the cake
Mix the milk, coconut oil, vanilla, and eggs into the dry cake mix (if you've made a large volume of mix, measure out a scant 4 1/2 cups cake mix). Mix well and beat for 2 minutes.
Scrape the batter into greased pans and bake at 350F for the estimated time listed below until a toothpick comes out clean or until the cake springs back when touched lightly near the center.
Let cool in the pan for about 15 minutes; then invert onto a rack to cool completely. Store cake or cupcakes in an airtight resealable plastic bag or other airtight container for up to 5 days.
Notes
Makes one 9" x 13" cake, two 9" round cakes, 24 cupcakes, or 36 mini-cupcakes