Fastnacht bread with sweet potato サツマイモ ”ファストナハト” ケーキ

My wife is a devotee of Japanese sweet potato "Satsuma-imo" サツマイモ. Whenever she sees it at our near-by Whole Foods, she will get some. The most common way we enjoy Japanese sweet potato is cooking it wrapped in aluminum foil on the Weber grill when we are cooking either chicken or pork roast (using indirect heat). She usually mashes the potato and adds soy sauce and butter. Then using the left-over mashed sweet potato, I make croquets (with ground pork, onion and shiitake mushroom) which is great (I have posted it). She has also used the mashed sweet potatoes to make gnocchi. This was a really good preparation because the sweetness combined with the saltiness of the soy sauce comes through very nicely. This time, my wife decided to make her "Fastnacht cake" using the mashed sweet potato. Her thinking was 'the recipe used regular mashed potatoes so how would it taste if I substituted the sweet potato?' She also modified the way she incorporated the " rivals*” and gave the bread a second rise which was not called for in the original recipe.

*According to the wikipedia definition of rivels, they are a type of spaetzle like small dumpling put in a soup. In the context of this fastnact cake, "rivels" are a sweet sugar crumb topping. (My wife did not make up this terminology. According to the ancient Pa Dutch cookbook she uses they specifically say "top with rivels" then give explicit instructions on another page under the heading of sugar topping. These include brown sugar topping, streusel topping and rivels. The main difference between them being the ratio of sugar, butter and flour).

The rivels are a crucial part of the cake. They are nice and crunchy and sweet. The problem is many of them fall off when they are put on the top and you end up picking up the crumbs eating them separately from the cake. She wanted the rivels to be a part of the cake. So, she decided to put a layer of rivels in the center. (pictured below). With this innovation, the rivels still come off the top and you still end up picking up crumbs (which apparently is just an inevitable part of enjoying this cake) but in addition there is now a guaranteed layer of lovely sweetness in each bite from the layer in the center of the cake.

Ingredients:
1/2 cup HOT mashed sweet potato (please note the recipe specifies HOT)
1 1/2 cup milk
1/2 cup butter
1 egg
1/2 cup sugar
2 tsp. salt
1/2 tsp. nutmeg
1 pkg active dry yeast
1/4 cup warm water if blooming the yeast
4 cups of AP flour to start, adding more as needed to make velvety dough.

Ingredients and directions for rivels (Crumb topping)
Mix together 1/2 cup sugar, 1/2 cup flour and 4 tbs. butter softened until the ingredients are completely combined and look like fine crumbs.

Directions:
Put the hot mashed potatoes into the bowl of a stand mixer. Using a mixing paddle beat in the butter, then the egg and a mixture of sugar, salt and nutmeg. Beat until fluffy. Bloom the yeast in warm water.
Beat the yeast into the potato mixture. Switch to a dough hook and alternately add the flour and milk beating well after each addition. If necessary add more flour to make a soft dough. Knead the dough on a floured surface until smooth and satiny. Put into a greased bowl. Grease the top of the dough, cover and let rise in a warm place until doubled.

Punch down the dough. Since the recipe makes two cakes split the dough into quarters so the rivals can be put into the middle of the cake. Then put 1/4 of the dough in the bottom of the pan, sprinkle on 1/4 of the rivels and top it with another quarter of dough (#1). Do this for both cakes. Brush the tops with melted butter and cover both with the remaining rivels (#2).  Let the cakes rise in a warm place for about 30 to 40 minutes while the oven preheats. Cook in a 400 degree oven for about 20 minutes or until golden brown.  The third picture shows the cake as it came out of the oven. And #4 shows the cake sliced. 

Both the use of the Japanese sweet potato, adding rivels to the center of the cakes and giving the cakes a second rise worked out well.  These were the the best fastnacht cakes ever—or at least the best my wife ever made. The sweet potato is completely substitutable for regular potatoes. The texture, however, was much better than the original recipe. It was much fluffier, more tender and slightly sweeter. The rivels in the center amalgamated into the  texture of the cake. But they also provided a moist layer of sweetness that was very pleasant. This may be the primary way my wife makes this cake in the future.