In a large measuring cup, we microwave the cold butter on 10% power until softened. This takes a minute or two. We do this in 30 second intervals since we do not want the butter melted, just soft. We put the butter in the KitchenAid, turn onto speed 2, and after 30 seconds, add 1 cup of sugar. We turn the mixer to speed 4 and cream the butter and sugar together for a few minutes until fluffy.
While the butter and sugar are mixing, we mix the topping ingredients—the 1/3 cup of remaining sugar, the brown sugar and the cinnamon—in a medium bowl with a fork.
Next, we add the eggs, one at a time, to the KitchenAid, mixing well. We turn the mixer off and scrape down the sides with a rubber spatula. At this point we stir in the vanilla.
We dump the flour mixture onto a large piece of parchment. With the mixer set at stir speed, we carefully add a third of the flour, then a third of the sour cream. We continue adding the remaining flour and sour cream mixtures until the batter is just combined. We turn off and scrape down the bowl.
We spray our oblong baking pan (8.875 inches by 12.625 inches) with Pam, put in a large piece of parchment to cover the bottom and a bit of the sides, and spray again.
We add the batter to the pan and dump on half of the topping mix. We swirl this sugar mixture into the batter with a fork and then add the rest of the topping distributed over the top and swirling it on the top with the fork.
We bake the cake for about 35 minutes until a cake tester comes out clean. We transfer the pan to a cooling rack and cool for at least half an hour before lifting the parchment out of the pan and cutting the cake with a heart cookie cutter.