(French). To put lard or fat between layers of meat. Metaphorically, to mix what is the solid part of a discourse with fulsome and irrelevant matter. Thus we say, “To interland with oaths,” to “interlard with compliments,” etc.
They interlard their native drinks with choice Of strongest brandy.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894