Q. The Mishnah Berurah (O”H 280:1) says that it is obligatory to consume garlic on Friday or Friday night. How is the garlic supposed to be prepared and how many cloves should be ingested?

A. Mishna Berura (ibid.) mentions that it is a mitzva. The Talmud (Bava Kama 82a) counts it as one of the ten enactments of Ezra. However, as we know not all of them are kept by all today. Aruch Hashulchan (ibid. 2) and Machazik Brocho maintain that it does not apply anymore today, Rambam also omitted it.
Mishna Berura quotes from Sefer Chasidim that we are dealing with fried garlic, since raw has an opposite effect. However, Orchois Ish and Orchois Rabbenu mention that the Chazon Ish and the Steipler Gaon zt”l would consume raw garlic when cooked was not available.
Horav Shlomo Miller’s Shlit”a opinion is that there is no shiur for the amount of garlic to be consumed, even a small piece will suffice.

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