I learned that the "secret Belgian" binding is Belgian, but not actually a secret. The creator of the structure prefers to call it the Criss-Cross Binding... But in America, the other name stuck. The book uses three pieces of book board and is sewn in two parts.
We started the class by folding signatures, and sewing together the textblock. Then we covered the boards with decorative paper. While the boards were drying, we sewed a practice card for the second part of the binding.
I am so glad we practiced the second sewing before attaching the textblock! It was pretty tricky to keep all the parts of the book in the right place during the sewing process. The "criss-cross" part comes from sewing back and forth over the spine piece at each set of holes along the spine. I really enjoyed the class and I'm definitely going to make more books like this in the future!