Preheat your oven to 350°F (175°C). Grease and flour three 9-inch round cake pans.
Cream the shortening and sugar together in a large mixing bowl until light and fluffy.
Add the eggs one at a time, beating well after each addition until the mixture is creamy and smooth.
In a small bowl, mix together the cocoa powder, red food coloring, and vanilla extract until it forms a smooth paste. Add this to the creamed mixture and mix until fully incorporated.
Sift together the flour and salt. Add this to the creamed mixture in three parts, alternating with the buttermilk. Begin and end with the flour mixture, and mix just until combined.
In a small bowl, combine the vinegar and baking soda. Quickly fold the foaming mixture into the cake batter.
Divide the batter evenly among the prepared cake pans.
Bake for 15-20 minutes, or until a toothpick inserted into the center comes out clean.
Cool the cakes in the pans for about 10 minutes before transferring them to a wire rack to cool completely.