Can I omit the chocolate without altering proportions? My sister wants an orange cake with chocolate buttercream (I can't convince her to go ganac...

yay! your sister is a lucky girl!

Great to hear; thanks for letting us know!

Made my butter cake with the zest of two oranges thrown in with the sugar and subbing a touch of the milk with fresh juice. It was great, definitely orange enough, and a hit. Thanks for all the advice!

I use citrus zests often in butter cakes; orange zest is pretty potent, so yes, I believe it will provide ample flavor to your cake. Removing cocoa from a chocolate cake throws the formula off balance for reasons beyond simply the flour. Since chocolate is an acid, chocolate cakes are leavened with baking soda. Removing the cocoa takes away half of what causes the production of carbon dioxide and would leave the cake with a soapy taste. You're much better off using your good, reliable butter cake and adding orange zest. If you substitute orange juice for the milk (and I don't think you need to do that), you're putting yourself back in the land of baking soda, which you'll need to add to neutralize the acid in the juice. Add it in a ratio of 1/2 teaspoon for every 8 ounces of acidic ingredient. The same goes if you sub buttermilk for the milk. Have a wonderful birthday celebration!

http://food52.com/recipes/8696-my-chocolate-orange-birthday-cake

p.s. as said by the others, you cannot just remove the cocoa powder. you prob would need to sub flour for it but dr babs will best know how to do that.

i would add a LOT of orange zest and grind it in a mini processor with the sugar to really get the flavor. and i'd also use OJ for part of liquid. do you have m stewart's Entertaining? she has an orange almond torte that i made for wedding cakes for 30 yrs. i added ground bittersweet chocolate bits to the cake and used a choc ganache between the layers and then a grand marnier buttercream over all. my personal fav cake (but then it's really a nut torte.)

Thank you Cynthia and Barbara. I have a yellow butter cake that is my go to birthday cake, but I've never converted it to a citrus cake. Cynthia, you think adding zest but not swapping orange juice for any of the liquid would do the trick? Thanks!

I agree with Cynthia. I'd add orange to Sdebrango's yellow cake, rather than leave the chocolate out of this one. Happy birthday to your sister!

You might consider making a different cake. Sdebrango's Tender Yellow Cake is lovely, and you can simply add orange zest to it. I imagine it would be heavenly with your chocolate buttercream. http://food52.com/recipes/11618-tender-yellow-cake