Apple-Cinnamon Crumb Coffee Cake

I brought this coffee cake with me to a neighborhood July 4th brunch, so it was actually the first cake of two cakes I ate at different July 4 festivities, but I actually made the tiramisu on July 3, so I blogged about it first.
What is not to like about a sour cream-apple coffee cake? It's an old standard for a good reason--everyone loves it. And it's easy enough to make that you can sleep in, read the paper and have a cup of coffee, mix it up and bake it, and let it cool--all in time to take it to a brunch.

This may be the closest I've come to so far to a cake that you could decide to make with ingredients you have at hand. It uses just one Granny Smith apple, so you can make it all year long, and if you've got walnuts and sour cream, you're all set.
The cinnamon crumb topping is actually both the topping and the filling--
one-half cup of walnuts, brown and white sugar, and cinnamon are reserved for the filling.

The flour and butter are added to the rest of the walnut-sugar mixture and this mixture is set aside, refrigerated, for the topping.
Layer some of the lovely, thick, sour cream batter in the bottom of a cake pan.

Sprinkle with the reserved filling and place a layer of apples on top of the filling.


Then top with the rest of the batter.

When I put it in the oven, Jim said, "Aren't you forgetting something?"
"Aha!" I said. "I am forgetting nothing!"
He thought that I had forgotten the topping, which was chilling in the refrigerator, but the clever twist on this coffee cake is that it's baked until it's about half done and THEN the topping is added. This way, the topping doesn't sink into the coffee cake and it also doesn't get too brown. And Jim will never know whether I actually forgot or not.
After 30 minutes, the cake is maybe 2/3 done.

You're supposed to form some of the crumb topping into tiny circular blobs, but I got bored with trying to form blobs of 1/4-inch diameter, so most of the topping has no man-made crumbles. I don't think was the wiser.

Can you count the number of crumbles that I laboriously pre-formed? I thought not.
I didn't check this recipe against the sour cream coffee cake in The Cake Bible, but it's certainly similar, except for the part about baking it for a while before adding the crumble. When I made The Cake Bible coffee cake, however, the bottom got too brown. This one turned out perfect. There are also variations - peach-cinnamon and blueberry-cinnamon, and it would be hard to go wrong with either of these.
But no more coffee cake for me--I have many, many cakes left to bake, and I can't afford to look back.