I would say No, I would use equal amounts buttermilk as milk, same measurement. But, you have baking powder in your ingredients so please read this:

If you find buttermilk's tang appealing you may want to replace some or all of the milk called for in certain recipes. When using baking powder, however, take care in substituting buttermilk for regular milk as it upsets the balance of alkali to acid. Buttermilk has more acid than regular milk, which will reduce the carbon dioxide released and thwart the leavening process important to these recipes.

To achieve the desired result when using buttermilk instead of milk, be sure to substitute baking soda for some or all for of the baking powder. For each cup of buttermilk used in place of sweet milk, reduce the amount of baking powder by 2 teaspoons, and replace with 1/2 teaspoon of baking soda.

*And I should add I'm hardly a professional baker, just my untrained opinion. I just finished a cake using buttermilk, and it called for soda not powder. Old recipe, tried and true.

What I wondered was when my old standby, which is exactly like the Food Network recipe except for the amount of milk, only calls for 1 cup, why this one calls for 3/4 cup more. I thought maybe buttermilk did something different in a cake. I'm a bit worried about cake soup.

I’ll be interested to see how this turns out.

I made a chocolate cake yesterday that the final step in the batter was to slowly add 1c of boiling water. I decided that since it’s hot and humid here I would adjust it. I ended up doing just a half cup of hot water. When the batter seemed like it was getting too soupy I stopped adding the water. It seems to have worked out but I’ll know tonight when we try it.

I baked the cake and used all the buttermilk called for. It was good -- very moist and heavy. I like heavy, but some might not. Several people ate two pieces and my grandson asked if he could have the same cake for his birthday -- only with blue icing instead of orange. So it was successful. I still don't know what the difference is between the amounts of milk and will probably do another with only the one cup, using buttermilk to see what happens. Thanks for the responses.

thanks for the follow-up, norar_il. It sounds like the amount of liquid contributed to it being more moist and heavier than your usual recipe. Do you have your recipe on a card or something you can make notes on?

Buttermilk tends to make the cake heavier (moister) than regular milk. It's usually my desired result..I hate dry cake.

Me too! We left the cake for the birthday girl, but I do have some buttermilk left . . .

I do have it written down and will make a note on it. Thanks for the reminder.

I've made what is probably the same cake as Annette with 1 C. of boiling water (Hershey's perfectly chocolate chocolate cake). Fortunately, the recipe did say that the batter would be very thin. I used the whole cup of water and it was scary but delicious. Nora, usually the amount of reg. or buttermilk in a recipe is the same. In fact , most recipes will tell you if you do not have buttermilk, you can add a T. vinegar to reg. milk. Also, you can freeze the leftover buttermilk and use it in your grandson's cake. :-)))