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I adapted the classic crumb cake recipe from my copy of Martha Stewart's Baking Handbook. It yields two dozen individual cakes. For the crumb topping you will need 3 c. flour, 1 c. packed light brown sugar, 1 tbsp. ground cinnamon, 1 1/2 tsp. coarse salt and 1 3/4 c. COLD unsalted butter. The original recipe calls for room temperature butter, but that is too warm to create a crumb texture in a stand mixer, which is what I used. So, make sure your butter is good and cold. You will end up with a little bit of left over crumb mixture, just f.y.i.
For the cake batter you will need 10 tbsp. unsalted butter (room temperature) plus more to grease the pans, 2 1/2 c. flour, 1 tsp. baking soda, 1 tsp. baking powder, 1/2 tsp. salt, 1 c. granulated sugar, 3 large eggs, 1 tsp. vanilla, 1 1/4 c. sour cream and powdered sugar for dusting the tops of the crumb cakes (optional).
Start by making the crumb topping. In the bowl of a stand mixer, sift together the 3 c. flour, 1 c. packed light brown sugar, 1 tbsp. cinnamon and 1 1/2 tsp. coarse salt with a whisk. Cut the (very cold) 1 3/4 c. butter into chunks and add to the dry mixture. Run the mixer on a medium setting until you start to see a crumb texture in the bowl. Keep a very close eye on the mixture to be sure stays crumby and doesn't start sticking together too much. Don't over mix.
Set the crumb mixture aside. Preheat the oven to 350º. Grease four donut pans with unsalted butter and set aside as well.
In a clean stand mixer bowl, cream together the 10 tbsp. (room temperature) butter and 1 c. granulated sugar until light and fluffy, three to four minutes.
Add the three eggs one at a time, incorporating each one fully into the mixture before adding another. Mix in the vanilla. Add the flour mixture a little at a time, then finally add in the sour cream and mix until just combined.
Spoon the batter into the greased donut pan cavities. Fill each ONLY just a hair over half way full. More than that and your crumb topping will get pushed all around as the batter rises. Smooth the tops of each with the back of a small spoon.
Sprinkle the crumb topping on top of each donut-shaped cake. There will be enough that you can get a nice, dense topping on each one. Clear the centers free of crumb with your fingers.
Bake for 20-22 minutes. Start watching around 20 minutes to be sure nothing is getting too dark, especially if you are baking four pans at a time and some are on the bottom rack in the oven. You want to brown them a bit, but not enough to burn them or even dry them out too much. A toothpick inserted into the cake will come out clean when done. Let cool completely in the pans.
When the crumb cakes have completely cooled, they slip out of the pans easily when gently coaxed with a butter knife.
Dust them with powdered sugar and serve with coffee (or not). Amazing. These keep a few days in a tight container on the counter, a few more in the fridge. I gave a dozen of them away right off the bat to keep us safe from eating too many of them. Delicious!