Preheat oven to 350 degrees.

In a bowl, whisk together all-purpose flour, sugar, unsweetened cocoa powder, baking soda, and coarse salt.

Make a well in center of flour mixture and add vegetable oil, pure vanilla extract, white vinegar, and cold water.

Whisk until well combined.

In two prepared 8 inch pans, divide the batter evenly.

Bake until a toothpick inserted in center comes out clean, 35 to 40 minutes. Let cool completely in pan on a wire rack

Place everything in a heavy saucepan. Cook over low heat, stirring constantly with a rubber spatula, until combined and thickened, between 20 and 25 minutes. Increase the heat to medium low; cook, stirring, 3 minutes more. Remove pan from heat.

Transfer frosting to a large metal bowl. Chill until cool enough to spread, about 2 hours, checking and stirring every 15 to 20 minutes. Use immediately once it reaches spreading consistency.