Beijus are common throughout Brazil and come in different ways. At least in areas like Bahia they will call them tapioca pancakes and will stuff them with different things, especially at hotels. Often they are just eaten simply with some butter spread on it. Or you can get real fancy and break into chip/cracker size pieces and put caviar on them.
Ok, now how do you make it? It is actually very easy, although everyone I know seems to have a hard time making it. It just takes practice and patience.
The fact is that goma seca is just another name for "polvilho azedo" or sour tapioca starch. If you live in the Us, there is no reason why you can't find polvilho azedo since you can always just get through the internet at site such as www. Sendexnet. Com. I've never had to try any substitutes so I don't know how good/bad any of them are.
First run the flour through a sieve several times (as if you were baking) and place in a bowl.
Now the trick is how much water to mix with the starch and this is just a matter of trial and error until you get the feel for it. Add water a bit at a time until you get the right consistency. Make sure to mix with your hand, not a spoon, because this is all about feeling for the right texture. You are aiming for a humid, yet loose, grainy flour. If you don't put enough it will be too dry. If you put too much, it will start to stick and feel a bit heavy. What I usually do is I keep putting water in slowly until it gets just beyond the point and then I throw in just a bit more flour to get it back to the right point.
To cook, heat a large flat bottom frying pan to medium-high. Make sure the pan is dry - do not put any oil or butter. Now the second trick - coat the bottom of the pan with the prepared flour by shaking through a sieve and onto the pan. Simply hold the sieve over the pan, throw in some flour and shake the sieve so you get a thin and even coating on the full bottom of the pan. What happens next is almost magic. After a few seconds, the flour will start to group together and form a pancake. Flip and cook on the other side. How much you cook is a matter of preference. In some parts of Brazil, they will toast it. I prefer it lightly cooked so it is still white.
This is the version common in Bahia.
Now you can put some butter on it and roll it up, or stuff it with ham & cheese, doce de leite or whatever else you wish.
Wipe the pan clean and do it again.
I'd be surprised if you get this right the first time, so don't get discouraged. If the first one doesn't work, it could be that you cooked too long or not long enough, so just try another one first altering the cooking time. More likely, however, it is because the flour is too wet or too dry. In particular, if the flour doesn't come together into a pancake, it is likely because it needs more water. It took me about 3-4 tries to get the feel for this, but since then they've always come out perfect and doesn't take much time too make since I know how much water to put in up front.