What is Zwieback toast and where can I find it?

Question

I am baking a black forest cake and it calls for zwieback toast. I cannot find this anywhere. Does anyone know what this is or where I can find it?

Answer

Zwieback toast is a twice-baked sweetened toast fed to teething children. It is also known as teething toast, and can be found in the baby aisle of most grocery stores.

Check more discussion of this question.