Why is it called coffee cake if there is no coffee in it?
Because it is meant to be eaten with coffee. The cinnamon streusel and buttery crumb are basically best friends with a mug of something hot.
Can I use Greek yogurt instead of sour cream?
Yes. Use full-fat plain Greek yogurt as a 1:1 swap. The crumb will be slightly tangier and sometimes a touch tighter, but still delicious.
How do I keep the streusel from sinking?
Two things help: make the batter thick enough by measuring flour correctly, and sprinkle streusel in an even layer rather than dumping it in a pile. Also, avoid overmixing the batter once flour goes in. One more tip: if your streusel looks greasy or heavy, stir in 1 to 2 tablespoons flour to bring it back to a nice crumb.
What pan should I use if I do not have a springform?
A 9-inch square pan works great. Grease it well and, if you want easy lifting, line it with a parchment sling. Bake time is often a bit shorter in metal, so start checking around 35 minutes, but do not be surprised if it needs closer to 45 to 55 minutes in glass or ceramic. The center should look set and spring back lightly.
Can I add nuts or fruit?
Absolutely. Add up to 3/4 cup chopped pecans or walnuts into the streusel, or fold 1 cup blueberries into the batter. If using fruit, toss it with a teaspoon of flour first to help prevent sinking.
