Q. Can you eat nuts when mixed in other foods like chocolate bars? Or even when grounded to a powder in a cake?

A. Beer Moshe (3: 97), Yad Yitzchok (1: 208) and others permit adding nuts when cooking food, if they are not recognizable. ( See Nitei Gavriel – Rosh Hashana 6: 8, and Piskei Teshuvos 583: 7, that many are stringent).
On question 213 we quoted Horav Shlomo Miller’s Shlit’a opinion that peanut butter is permitted.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a