Tip of my tongue: what is the name of this process?
The general term for the process would be "encapsulation".

The Wikipedia article on micro-encapsulation lists different processes by which such encapsulation is achieved. Two which sound similar to your described process are interfacial polycondensation and interfacial cross-linking:


  In interfacial polycondensation, the two reactants in a polycondensation meet at an interface and react rapidly. ... Condensed polymer walls form instantaneously at the interface of the emulsion droplets.


Alternatively, the process your class did might have been ionotropic gelation:


  Ionotropic gelation occurs when units of uric acid in the chains of the polymer alginate crosslink with multivalent cations.