Begin by prepping your pan and oven, greasing either a 9x13-inch pan or two 8-inch round pans, and preheating your oven to 350°F. In a large mixing bowl, combine 2 cups sugar, 3 cups flour, 4 tablespoons cocoa, 2 teaspoons baking soda, and 1/2 teaspoon salt.
Whisk these dry ingredients together to guarantee even distribution of the leavening agent and cocoa. Next, add 3/4 cup vegetable oil, 2 tablespoons vinegar, 2 cups water, and 1 teaspoon vanilla to the dry mixture. The batter will be noticeably runny—this is normal and necessary for the cake's moisture. Mix on medium speed for 2 minutes until the ingredients are well combined, then pour the batter into your prepared pan(s).
Bake at 350°F for 35 to 40 minutes, or until a toothpick inserted in the center comes out clean. The baking time may vary slightly depending on your oven and whether you're using one larger pan or two smaller ones.
Once baked, remove the cake from the oven and allow it to cool completely before frosting. This cooling step is essential, as frosting a warm cake will cause it to melt and slide off.
While the cake cools, prepare the frosting by cooking 4 tablespoons flour and 1 cup milk together over medium heat, stirring constantly until the mixture thickens into a pudding-like consistency.
Set this cooked mixture aside to cool completely. In a large bowl, beat 1/2 cup margarine and 1/2 cup Crisco together for 4 minutes until creamy, then add 1 cup sugar and beat for another 4 minutes.
Stir in the cooled cooked flour mixture and 2 teaspoons vanilla, then beat for a final 4 minutes until the frosting reaches a smooth, spreadable consistency.
Once the cake is completely cool, frost generously, creating decorative swirls on top and finishing with chocolate shavings or sliced strawberries for an elegant presentation.