Q. The minhag of our family is to abstain from eating nuts the complete Aseres Yemei Teshuva, can I eat in a kiddush a cake that contains nuts?
A. On question1843 regarding the extend of the minhag of eating nuts, we wrote: "There are different minhogim mentioned by Poskim regarding the time one keeps this tradition.
From Remoh’s (O.H. 583: 2) citation of the minhag, it would seem that it applies only to Rosh Hashono. However, Nitei Gavriel (Rosh Hashana 6: 8, quoting Beis Hayotzer and others) mentions that some observe it during the whole month of Elul until Hoshano Rabbo. Others maintain only from the beginning of selichos (Ktzei Hamateh and others). Chassam Soffer would restrict the minhag only to Rosh Hashono itself, while his Rebbe, Horav Nosson Adler zt’l only until the second day at chatzos. (Piskei Teshuvos 583: 7). See next question in regards to the reasons of this tradition.
Horav Shlomo Miller’s Shlit’a opinion is that one should maintain his family’s and community traditions."
Beer Moshe (3: 97) tends to be lenient on foods that have nuts mixed into them when not in Rosh Hashono, however he mentions that the one who is stringent deserves blessings. (See also Piskei Teshuvos 583: 7).
Horav Shlomo Miller's Shlit'a opinion is that although in our case there is place to be lenient, in principle each individual should maintain the traditions and minhogim of his family and community.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit'a