Recursive definition of a language $ L $ over $ \{a,b\} $ How would I start the recursive definition of the following language:

L over {a, b} such that L consists of strings in which each
occurrence of b is immediately preceded and followed by an a

The 'and' part is causing me problems with this problem and I don't see a clean way to gurantee the occurence being preceeded and followed recursively.
The recursive definition structure is as follows:
Basis: The base we have to start with for the recursion
Recursive step: How we generat ethe language from the basis
Closure: Trivial to state
My thought process on this:
We can have lambda, because no b's or no a's doesn't apply to the condition.
My attempt so far:

Basis: $ \lambda \in L $
Recursive Step: If $ w\in L $ then $ aw, wa, babw, waba \in L $.

What i don't see is how th break the recursive step to account for being able to place b's anywhere in $ w\in L$ such that the condition is satisfied.
There is no problem to obtain $b$'s anywhere in the string: basically you can just "read" the string from left to right, and add the $aba$ to the end. That leaves one with only two recursive steps: if $w\in L$, then $wa\in L$ and $waba\in L$. 

A bigger problem is that you now do not generate strings like $ababababa$!

This can be handled by having rules like: if the string ends with a $a$ we can add $ba$ to the end.