Vanilla Yogurt Coffee Cake

Successful Baking for Flavor and Texture (1934) won me over with its gorgeous pink cover. I found a simple coffee cake recipe there and I substituted oil for the butter and added a couple of egg yolks to make it as moist as possible. With Greek yogurt so popular these days, I decided to use it instead of buttermilk—it gives the cake a wonderful tang. I also added a generous amount of vanilla (strangely, the original recipe called for none!). A buttery