May one eat biscuits, cakes, and the like, which have words/letters engraved on them?
To break it and then eat it: It is forbidden to break the letters that are on a food, even if the letters are engraved. Accordingly, one may not break a piece off from the cake or biscuit if doing so entails breaking one of the letters.
To take a bite out from it: Some Poskim rule that one may break engraved letters within the process of eating. Meaning, that one may break the letters in the process of taking a bite from the food, and the prohibition is only against breaking it with one’s hands and then placing it into one’s mouth. However, other Poskim rule they may not be broken even within the process of eating. According to this latter opinion, one may not give such foods to children that have reached the age of Chinuch. Practically, one is to speak to his Rav for a final ruling.
 Ketzos Hashulchan 144 footnote 3
 Admur 458:8 “The symbols which are made on the Matzos should not be made through forms of letters using a molded imprint [i.e. cookie cutter], or with one’s hands (for the reason explained in chapter 470 and others) being that one is required to break them on Yom Tov, and there are opinions who prohibit to break a cake which has forms of letters on it even though he does not intend to erase the letters, but rather to eat them on Yom Tov, as was explained in chapter 340. Rather these symbols are to be made through holes or grooves, as long as one is careful to extremely speed their process, as was explained in chapter 460, see there.”; Teshuvas Rama; Chok Yaakov 475; Levush
Other opinions: Some Poskim rule the erasing prohibition does not apply to the engraved letters that are on a food. [Ra”sh Haleivi brought in Magen Avraham 340:6, although he himself concludes with Tzaruch Iyun; Maharil; M”B 340:15; SSH”K 11:8]
 The reason: This is Rabbinically forbidden to erase letters on Shabbos even if one does not plan to write any letters in its place. [Admur 340/4]
The reason behind the leniency of engraved letters over external letters according to the lenient opinion: Engraved letters are not common today, and thus, since one has no intent to write in the area that the letters are erased, in which case it is at the very most only a Rabbinical prohibition, therefore, one may be lenient to erase engraved letters, as the Sages did not make their decree in uncommon cases. The Sages did not suspect that one may come to erase engraving with intent to write in its place. [Ketzos Hashulchan 144 footnote 3]
 Ketzos Hashulchan 144 footnote 3 [His final ruling is written on page 151 at the end of the paragraph]; Shabbos Kehalacha Volume 3 p. 369; 20:73 [To note that the Ketzos Hashulchan did not mention this ruling in chapter 144 and only later was it mentioned by him in the glosses to the end of the 7th volume, nevertheless, it is implied from there that his conclusion is to allow breaking the letters in the process of eating. See however the case of a bottle cap with engraved letters that the Ketzos Hashulchan allows one to break it on Shabbos, although contradicts himself in the glosses to the end of volume 7. Vetzaruch Iyun. The Rebbe was once addressed this question of whether one may break engraved letters according to Admur, and the Rebbe answered that no conclusive stance can be taken on this issue. Vetzaruch Iyun, being that this matter is explicitly ruled on in Admur 458:8]
 The reason: The basis of this ruling is that a) There are Poskim [Degul Merivava 340] who always allow breaking all letters within the process of eating [chewing it] and b) There are Poskim [brought in previous footnote] who allow breaking engraved letters even with one’s hands. Thus, although Admur rules stringently regarding on breaking within process of eating [with regards to letters written with icing], while the Magen Avraham leaves in question regarding breaking engraved letters, when both leniencies are combined, such as breaking engraved letters of a biscuit within the process of eating, then one may be lenient. [Ketzos Hashulchan ibid] This seemingly holds true as well in accordance to the ruling of Admur in Hilchos Pesach 458:8 who forbids breaking the Matzah with engraved letters, implying that taking a bite from it is allowed.
 Rav Bitstritzky in Shut Ara Degalil p. 35; Piskeiy Teshuvos 340 that from Admur ibid it is implied that this too is forbidden; Rav Eliyahu Landa that the custom is to be careful not to eat such foods on Shabbos.
 Rav Bistritzky does not make mention of the ruling of the Ketzos Hashulchan throughout his entire ruling. However, at the end in a footnote he mentions that he found a ruling of the Ketzos Hashulchan which contradicts his ruling, and he writes that seemingly the Ketzos Hashulchan forgot the ruling of Admur in 458:8. However, in truth the Ketzos Hashulchan in his Hosafos does add the ruling of Admur there and nevertheless does not retract his final ruling said above.