‘Achar’ is actually a Hindi/Urdu (Hindi: अचार, Urdu: اچار,) word for pickles; see here. It’s also spelt as acha, achaar, or acar in modern Malay spelling. The origins of the word also tell us about the diffusion of foods from South to Southeast Asia.
Here’s the basic barebones acha/achar recipe.
And several pages further on in the notebook, there are more acha notes: