Sweet Potato Cake with Brown Sugar Cinnamon Swiss Buttercream

It is happy birthday time again (does this seem to be getting a little ridiculous?  All the birthdays?).  This time, however, the birthday belongs to your humble blogger...me.  Yes, another year has ticked by, and I might be still a little bit in denial.  So what do I do about it?  Make a big fat luscious cake and eat it all by myself.  Well, all but the eat it all by myself part.  This year's birthday falls during some interesting circumstances that are ending with another move.  So, the debate: super easy low key sheet cake with a quick frosting since no one is around to share and half of my house is empty (the empty house doesn't really have any bearing on it, but it sounded good).  OR...a spiced sweet potato cake with a fluffy toffee and marshmallow filling topped with a decadent brown sugar cinnamon Swiss buttercream.  Um yeah.  If you're going to get old, eat good cake!!!


The cake has a delicious sweet potato flavor, with warm spices.  Sandwiched between the layers is a marshmallow filling with toffee bits.  And the crowning glory??? Swiss Buttercream!  I was nervous about making this buttercream, because I haven't always had this best luck with non-american buttercream (American buttercream uses powdered sugar).  This time, however, the results were absolutely perfect.  Amazing. A thing of beauty.  Can you tell I'm a little proud of myself?  Anyhow, quick note on the cake layers.  I used an 8 inch round corningware baking dish, and a 6 inch corningware baking dish.  Why? Because I don't have cake pans in that size, and I had to MacGyver it.  Worked out pretty well, don't you think?


Sweet Potato Cake with Brown Sugar Cinnamon Swiss Buttercream


Cake:
2 large eggs
1 cup sugar
1/2 cup (1 stick) + 2 Tablespoons butter, melted and cooled
1 pound cooked, mashed sweet potato
1 teaspoon vanilla extract
1 cup (4 ounces) cake flour
1 teaspoon baking powder
1/2 teaspoon salt
1 1/2 Tablespoons cinnamon
1/2 teaspoon nutmeg
1/4 teaspoon ground ginger


Toffee Marshmallow Filling:
2 7-ounce containers of marshmallow fluff
1 cup shortening
2/3 cup powdered sugar
1 1/2 teaspoons vanilla extract
pinch of salt
4 teaspoons very hot water
2/3 cup toffee bits


Brown Sugar Cinnamon Swiss Buttercream:
2 large egg whites (2.5 ounces)
1/2 cup + 2 Tablespoons light brown sugar
3/4 cup (1 1/2 sticks) butter, softened and cubed
pinch of salt
dash of cinnamon, to taste
1 teaspoon vanilla extract


Preheat oven to 350F.  Grease and flour an 8 inch round baking pan and a 6 inch round baking pan (or corningware, as it were).  In the bowl of a stand mixer fitted with the paddle attachment, beat the eggs and sugar together on medium-high speed until light colored and very smooth.  Add the melted cooled butter, and the mashed sweet potato, and vanilla and mix until combined.  In a small bowl, stir together the flour, baking powder, salt, cinnamon, nutmeg, and ginger.  Add to the sweet potato mixture and beat on low until just combined.  


Pour the batter into the prepared pans and smooth the tops.  Bake until a toothpick inserted in the center of each cake comes out clean, about 20-25 minutes for the small cake, 40-45 minutes for the larger cake.  Let pans cool for about 10 minuets on a cooling rack, then turn the cakes out of the pans onto the rack and cool completely.


For the marshmallow filling, in a medium bowl combine the marshmallow fluff, shortening, powdered sugar, vanilla and salt.  Using a hand mixer, beat the ingredients together until combined.  Beat in the hot water, then add the toffee bits and beat until completely combined.  Set aside.


For the Swiss Buttercream, combine the egg whites and brown sugar in the bowl of a stand mixer.  Set the bowl over a pot of simmering water (do not let the water touch the bottom of the bowl), and whisk constantly until the temperature reaches 160F, or the sugar has dissolved completely, and the egg whites are hot.  


Return the bowl to the mixer and with the whisk attachment, whip the egg/sugar mixture until it is a smooth, thick, and glossy meringue, and the bottom of the bowl feels about room temperature.  Switch to the paddle attachment and with the mixer on low speed, slowly add the butter, about a tablespoon at a time until all the butter has been incorporated and the buttercream is silky and smooth (this took me about 10 minutes, so be patient).  If the buttercream looks curdled, continue beating on low speed until it comes back together.  Add the salt, cinnamon, and vanilla, and beat on low speed until combined.


To assemble the cake, trim the domes off the top of the cakes, then slice each cake layer in half horizontally to make two large and two small layers.  Place a small spoonful of marshmallow filling on the center of a serving plate.  Place the bottom piece of the large layer on the serving plate.  Spread with the marshmallow filling, then place the other large layer upside down on top.  Spread a small amount of filling in the center of the cake, then top with the bottom of the small cake layer.  Spread with the marshmallow filling, then place the remaining layer upside down on top of the filling.  Frost the tops and sides of the cake with the swiss buttercream.  Store cake in the refrigerator, and bring to room temperature before serving.  Makes one small cake, about 8 to 10 servings.  Original recipe found here.


Enjoy!  -Cardamommy