Formula to calculate Cepstral coefficients (not MFCC)
Linear Prediction Cepstral Coefficients (LPCC) can easily be computed from LPC (Linear Prediction Coefficients) and I think that a LPC function is implemented in the same package as the MFCC.

All you need to know for extracting $p + 1$ first LPC is here. The formula that link LPC and LPCC is:

$c_0 = ln(p)$

$c_1 = a_1$

$c_i = -a_i + \sum_{n=1}^{i-1}\frac{n}{i}a_{i-n}c_n$ for $1 &lt; i \leq p$

where $c_i$ are the LPCC and $a_i$ the LPC and $p$ the order (i.e. the number of coefficients - 1). I'm not sure about the negative sign before $a_1$. Reference here.

I'm not sure what you mean with 'windowing' but yes it may be necessary depending on your signal and application.

Hope that it will help.