Purple Yam Swiss Roll

I've seen purple yams/sweet potatoes used in many Filipino desserts here in Vancouver but I had never tried one myself. A vegetable as a dessert? Hmmm not sure about that ;) 

The thing that stands out the most is obviously the colour! I've never seen such a beautiful purple from a natural source before! Once steamed it is very sweet - more so than a traditional yam/sweet potato, I think - so it really does work well in desserts. The texture was certainly different than what I am used to in a dessert and at room temperature it wasn't my favorite BUT once refrigerated for a couple of hours it was great AND after our first night I froze the left overs and the next day it was heaven! It was very much like an ice cream cake! YUM.

Love the colour!

Roll the cake from the short end and leave half an inch of no filling at the
far side so it doesn't squish out.

Cut off the ends if you want a cleaner presentation.

I brushed some purple food gel onto my silpat
thinking it would  blend into the batter - it didn't!
But I  still like it!

So pretty!

I liked the texture best when frozen for a few hours.

Swiss Roll Cake (based on a recipe by Rose Levy Beranbaum)

1/4 cup (33 grams) whole wheat pastry flour
2-1/2 tbsp cornstarch
4 large eggs, at room temperature
1 large egg yolk
1/2 cup sugar + 1 tbsp sugar
1 tsp vanilla
1/4 tsp cream of tartar
icing sugar for dusting

Instructions

1. Preheat oven to 450 degrees F.
2. Using a half-sheet pan (17-1/4 x 12-1/4) coat with non stick spray then place a silpat or nonstick liner on the pan. Spray the silpat with baking spray the contains flour.
3. Separate 2 eggs, and place the yolks in a mixer stand bowl and the whites in another bowl and set aside.
4. To the yolks add the two whole eggs, 1/2 c sugar and one more egg yolk. Beat this at high speed for 5 minutes. Add vanilla and mix in at medium speed. 
5. You need the mixing bowl again so place the yolk mixture into another bowl. Clean the original mixer bowl really well as any fat left in the bowl will affect the beating of the egg whites.
6. In a small bowl, whisk the flour and the cornstarch.
7. Sift half the flour mixture over the egg yolk mixture. Fold it in very gently. Repeat with the remaining half of the flour.
8. In the large, cleaned stand mixer bowl add the egg whites. Using the whisk attachment beat the whites on medium speed until they are foamy. Add the cream of tartar. Increase the speed to medium high and beat until the whites form soft peaks. Add 1 tbsp sugar and beat until stiff peaks form when whisk attachment is lifted. Fold the whites into the yolk mixture. 
9. Pour the batter onto the baking sheet and smooth with an offset spatula. 
10. Bake for 7-8 minutes until golden brown.
11. Immediately loosen the sides of the cake from the sides of the pan. Gently slide the liner and cake out of the pan and on to a work surface. Sift the icing sugar over the cake. While hot, roll the cake from the short end making sure you include the liner as you roll. 
12. Set the cake on a wire rack to cool for 45 minutes.

Purple Yam Mixture

1-1/2 cups purple sweet potatoes, peeled cut and steamed (they need to be hot)
3 tbsp butter
1/3 cup icing sugar
2 tbsp cream cheese
1/2 c whipping cream

Instructions

Using food processor with the steel blade attached, add all the ingredients. Process until smooth. Refrigerate for 30 minutes.

Putting it all together

Unroll the cake and carefully detach the cake form the liner and them lay it back on the liner again. 

Spread the potato mixture evenly over the cake leaving 1/2 inch of no icing on one short end. Starting at the other end, tightly and firmly roll the cake. Place on a serving plate with seam side down. Refrigerate or freeze for at least an hour before serving.