The blu-ubé ricotta roll-up cake

My Manila friends will know and readily attest to my obsession with ubé–the purple yam that is used to flavor ice creams that top that most iconic of Filipino desserts, halo halo. Knowing Manila traffic makes it hard to get about anywhere, let alone to a wet market in search of these somewhat unfriendly-looking masses of yams, I’ve twice had very kind participants in courses I was teaching hand me purple yams as take-home souvenirs to feed my soul. “Half to cook with, half to plant,” I was told.

So, dutifully, I did both.

First, a confession and a disclaimer: I know nothing about growing yams. All the gardening I have done has been learned on the go, by trial and error, in between parenting and professional deadlines. Throw some seeds, stick what’s spoiling or sprouting into the ground, and above all hope–without expecting much. I knew only that the purple yam was, like so much else in life, forbidding and scary on the outside but stunning and other-worldy on the inside:

Yams are not sweet potatoes; botanically they’re related to lilies rather than potatoes and go by the name Dioscorea alata (kaand or ratalu in Western Indian states, where the yam is widely used in savory cooking, too. More on that in a future post). Ideally, to grow purple yams you need bulbils (aerial tubers) and not just the from-the-ground yam itself:

But having only two grumpy looking walrus-like tubers in my company…

I had no choice but to work with them. I cut them into chunks… 

Note: if roots are obvious, as with my yams, then they constitute a separate chunk. Though I suspect the one that grew in my garden in the end was one of the other chunks. 

I smeared them with ash to ensure that they had a chance to grow before the rodents and other garden creatures got to them…

And I set them in some well-draining soil. And I watered, and I waited.

In our case it took 5 long months (from October, when it starts to cool to April, when it warms here like a furnace), before my younger son and all-round garden forager spotted a strange new vine growing just where our tuber chunks had been:

It was unmistakably the ube; its purple tinges and heart-shaped leaves were a dead give-away. We couldn’t stop gawking, especially at it’s delicately frilly purple-edged helix-like curving stems…

For those of you wanting to try hands at yam-growing on any old trellis, there are a couple of good guides here and here. 

In the meantime, I found myself in Manila again, and again with a monster of a yam gifted to me to carry home [and thankfully not gifted in exchange for me–inside anthropology joke for those who’ve ever read about gender and gift-exchange..]. It was a sign from the universe itself that I had this new yam right when we spotted mine growing at last, so I lost no time in figuring out how to pay homage to Filipino traditions and bake a most excellent purple yam cake:

Except it wasn’t purple any more. It was distinctly blue. So we called it the blubé roll-up cake. 

This cake is essentially a chiffon baked in a jelly roll pan, a ricotta icing slathered on, and rolled.

But, back to the purple yam’s stunning-yet-elusive purple: although it stayed stable when the yam was ground to a paste…

… the color was already turning blueish during the final mixing, and was undeniably blue when the batter came to the jelly roll pan…

By the time the cake is baked and rolled, it’s blue that is dominant, the purple long-gone, lost to kitchen chemistry.

Note: Most Filipino recipes will call for 1/2 teaspoon or such of ube flavor and violet coloring. Now ube flavor already comes colored, so why add even more? With color or without, the mystery of disappearing purple remains yet to be solved…  The addition of baking soda quite quickly turns the purple into blue, which tells me that ube color is PH-sensitive. Ube makes the chiffon dense, so it seems hard to eliminate the small quantity of baking soda this recipe uses, but I’ll try soon and report back. For now, however, the cake stays blue: 

Quite resembling a nautilus-like strange sea-creature…

.. with a pure white creamy heart, of course.

If you’re wondering what the green flecks are, they’re the zest of another Filipino treasure, the common green orange called dalandan (Citrus aurantium):

Although really, the zest of any good green lime will do just fine to give that little citrusy punch to the ricotta frosting. Ready to blubé yourself? Read on, for the full recipe.