The batter for this cake was like a big, overflowing bowl of clouds - light, billow-y and smooth, made using cake flour to ensure the cake will have a lovely tender crumb. I do recommend purchasing cake flour if you don't already have some handy - brands I've used numerous times before are Softasilk and Swan's Down, but I've recently just started using King Arthur's branded unbleached version and have found it works just as well, though the texture is not as ultra-fine. You could always try the common substitution of using all-purpose flour, taking out 2 tablespoons for every cup and replacing them with cornstarch, but I haven't personally used that method.
To give the cake some character, a crumbly streusel is scattered not only on top of the cake, but also used as a hidden layer inside. Half of the batter is spread into a tube pan, followed by the sugar-y crumbles made by working cold cubes of butter into a mixture of flour, brown sugar and cinnamon. For a bit of crunch, walnuts are also stirred into the streusel - pecans would be a good choice here too. I did double the recipe from the original as who doesn't love a boatload of streusel, but feel free to cut those ingredients in half for a lighter touch.
After the cake has baked and had a chance to cool, it easily released from the pan (have to love those two-piece tube pans for that reason alone), we had one more job to do before we called this cake complete - a snazzy maple-laced drizzle! All this entails is stirring together confectioners' sugar with enough pure maple syrup to make a thin enough glaze, which is haphazardly dribbled all over the top and sides.
The sour cream made the crumb incredibly moist, but if you're not a fan of its natural tang, don't be concerned, it doesn't translate into the cake's flavor. Between the rich brown sugar, cinnamon and crunchy walnuts, the streusel does play a starring role here, which made doubling it make sense, but it may have led to an issue I wasn't expecting.
I am a little disappointed in how the cake rose - it was fine on the sides and center near the tube, but the center ring seemed to peter out and stall. I'm going to guess it was the weight of the doubled streusel, but I'm not completely sold on that - any guesses out there? Saying that, Jeff and I both seem to think it did not affect the texture that much (it was a bit more dense than it probably should have been) and the flavor was still spot on.
Sour Cream Coffee Cake