The basic formula for these cakes was developed by the wife of a mayonnaise salesman in an effort to help him out. I did a bit of research, and have found many variations. Early variants generally involve using less cocoa, which I cannot recommend. Later variants involve using cold water instead of boiling, adding salt, and additional leaveners. I personally do not feel that any additional salt is needed, as mayonnaise and that famous, tangy brand of salad dressing (sometimes the label just says 'Dressing') both contain a fair amount of salt. If you are using homemade mayonnaise or a low sodium product, an eighth teaspoon of salt may boost the flavor a bit. And, of course, somewhere along the way fans who prefer a certain salad dressing over mayonnaise started using it to make this cake. Nowadays, the Hellman's website has a different formula -one with added eggs and baking powder. I have not tried this newer formulation.
Some versions of this recipe specify sifted cake flour. This will result in a very light cake with virtually no structural integrity, due to the paucity of eggs in this recipe compared to a regular cake. Cupcakes made this way give beautifully light results. However, every time I try to make a traditional 8" double layer cake with cake flour, I experience collapse. I recommend AP flour or at least a mix of cake and pastry flour.
I have never made this with a gluten-free flour replacer. This recipe does not have very much structural integrity and as such does not make a good candidate for a gluten-free cake.
I have made this cake many times, the type of sandwich spread you choose will affect the outcome. Made with mayonnaise, the cake has a good chocolate flavor and moistness. Made with that famous, tangy, off-white salad dressing that gets used as a sandwich spread, the cake has a subtle bit of extra brightness to the flavor. If one chooses to use a vegan mayonnaise, the result is tasty but lacking a little in structure; I would bake this in a square pan and frost and serve from the pan.
The cocoa you use will also affect the flavor. For a classic, homey flavor use a supermarket brand of cocoa. To add a little sophistication, use better, artisan type cocoa and use chocolate extract instead of the vanilla extract.
Supposedly, the traditional frosting for this cake should have a caramel flavor. Look for one where you actually caramelize some sugar first. Modern recipes for the icing seem like weak imitations to me; using brown sugar as the main flavor instead of true caramel.
Chocolate Mayonnaise or Salad Dressing Cake
makes enough for two 8" round pans, or a 9" square (about 7 cups of batter)
2 ounces/56g unsweetened, non-alkalized cocoa
1 cup/236g boiling water
1 teaspoon/4g regular strength vanilla extract
3/4 cup/162g mayonnaise, vegan mayonnaise, or salad dressing (the tangy, off-white, sandwich spread type dressing)
10.5ounces/300g all-purpose flour
7 ounces/200g sugar
0.35ounce/10g baking soda
Preheat your oven to 350°.
Grease or spray two 8" round pans or an equivalent volume square or rectangle.
Place the cocoa in a medium (4-5 cup) bowl. Add the hot water and stir with a fork to break up any clumps. Allow to cool down a little, then add the vanilla extract and the mayonnaise or salad dressing spread. Beat well to eliminate lumps. In the bowl of an electric mixer or larger regular bowl if making by hand, sift in the flour and add the sugar and baking soda. Mix the dry ingredients to distribute evenly. Slowly beat in the cocoa mixture. Mix until the batter has an even color. Pour immediately into the pans. If making two 8" rounds, weigh them to ensure they contain equal amounts.
Bake for approximately 20 minutes, or until the center of the top springs back when touched lightly. (The toothpick test does NOT work well on this moist cake!) Allow the cake to cool a little and shrink from the sides of the pan before removing. Removal is easier while still a little warm.
Good with or without frosting.
Good beginner cake for kids to make.