I am not really sure what this is called. The first time I tasted what seemed like puto with filling like that of siopao, it was when a sister-in-law brought some from Laguna. I loved it then. She said it was called cuapao. The shape was rectangular.
With previous browsing on the net, some called it puto pao. The cua pao search I made led me to a photo that did not look like what my ex-SIL brought. So, I don't know what this is really called. But simply put, that pao that I had then from SIL is basically puto with siopao filling. Period.
Now, with my easy method of making puto from boxed white cake mix (and I recently bought a pint of pure pasteurized egg whites), I made some puto pao (or cua pao?). After my kids loved them paos, I thought I should have a set of rectangular or square silicone muffin cups. So I bought a set of square and triangular. Next time I make puto pao again, I will use the square ones(they are larger too than the typical muffin cup shape). We already tried them with brownies and once the brownies were cool enough, they were easy to remove from the silicone cups.
I used leftover beef pares for filling (note: the beef pares link will lead you to my blog post which had a very old unappealing photo of my beef pares, which does not do justice to how scrumptious this dish is, so please do not be discouraged. It has been a tried and tested and loved recipe by several of my readers, and a favorite special beef roast recipe in my household that even my in-laws love it). I chopped the meat roughly, mixed that with the sauce, adjusted the sauce with thickener (cornstarch-water mix), salt, sugar, pepper as necessary. Then I chilled the mixture prior to making the puto pao. The chilling enables me to shape the filling into disks which I could lay flat over half of the puto batter before I top with the other half.
I get the water boiling even before I start preparing the batter. I use any white cake mix in my pantry, with the required egg whites and oil, then mix thoroughly with a hand mixer until batter looks fluffy. I place about a teaspoon at the bottom of the muffin paper liner, then carefully top with flattened filling (I measure using cooking scoop), then finally add another teaspoon or so of white cake mix batter, or enough to cover sides and top of the filling (I avoid adding too much). The slide show has some photos with sliced cheese on top, or plain, or some puto pao with the filling on top only (I experimented to place the filling on top, expecting it to sink to the middle while steaming, but it did not).
The result got my kids excited, they had these for snacks that night, and saved some for the next morning for their breakfast.
As expected, hubby only ate the plain puto. :(