This is the type of coffeecake my mother often made when I was growing up. Enriched with sour cream and swirled with cinnamon and sugar, it is the perfect, after-the-fast treat. In fact, it’s great at any time! Now, for a lighter treat, my mother and I often use half sour cream and half yogurt, as in this version, and it’s still delicious, but you can use all sour cream if you prefer. You can bake it two to three days ahead, wrap it, and keep it at room temperature or in the refrigerator.