First, we didn't have any sour cream handy, so instead I replaced about half its volume with Greek yogurt. I also added about two tablespoons of "sourdough sponge," which works well in place of sour cream in many baking recipes. The instructions call for blending the sugar and butter for quite a while, but I only did it for two or three minutes--mostly by hand.
The only regrets... We were completely out of vanilla this morning, and I forgot to use the pecans we had in the freezer for the streusel. This might be a recipe to prepare the night before, if you want to actually eat it before you have to leave the house. In our case, it didn't work for breakfast, but it made for a lovely brunch.