Saying the blessing? One is to designate an area from the dough that the Challah will be separated from. Then one is to say the blessing “Lehafrish Challah”. One then separates a Kezayis of dough and says “Hareiy Zu Challah” or “This is Challah”. If one separated the Challah prior to the blessing one may still say the blessing if he [or she] has not yet said “Hareiy Zu Challah”.
What to do with the Challah: The separated piece of Challah is to be wrapped in tinfoil and burnt in the oven [or on the stove]. It is to be wrapped well to the point that the dough will not become revealed while being burnt, as Challah is forbidden to be eaten and thus burning it in the oven is similar to cooking a non-kosher food in one’s oven. Due to this reason one is to never bake any other foods in the oven until the Challah is burnt or removed. Alternatively rather than burning the Challah, one is to wrap the Challah and discard it in the garbage. Practically today this is the more preferred custom to follow due to a Kashrus worry that the tinfoil of the Challah may open prior to the Challah becoming fully burnt hence causing a Kashrus issue for the oven. Furthermore today most garbage is burnt and hence one regardless fulfills the Mitzvah of burning the Challah when discarding it in the trash, and there is thus no need to burn it in one’s Kosher oven.
 Rama 322/5
 Following the ruling of Rav Avraham Chaim Naah. However according to the Chazon Ish one separates 55 grams.
 Some have the custom to add “Min Haisa” [see Taz Yoreh Deah 328/1]
 As applies by all Mitzvahs that the blessing is said prior to the Mitzvah. [So writes Hakashrus 14/20; “Spice and Spirit”] However Piskeiy Teshuvos 242/11 records that one is to only say the blessing after completely separating the Challah from the rest of the dough in order so no part of the Challah remains on the dough if one were to separate it after the blessing.
 Hakashrus 14/21
 Hagahos Maimanis ibid
 The acronym of the name Chana stands for Challah; Nida and Hadlakas Neiros. In merit of her fulfilling these three Mitzvos properly she had her prayers answered and had a son Shmuel which was a prophet and leader onto Israel. Thus each woman should Daven upon separating Challah to have children that are proper and G-d fearing. [ibid]
 See Hakashrus 14/22; Piskeiy Teshuvos 242/11
 Yoreh Deah 322/5
 If the Challah became revealed in the oven prior to becoming burnt one is to contact a Rav. The answer to this question depends on whether the dough touched the oven floor, walls or oven grates.
 Some write the Challah is to be doubly wrapped. This is done for purposes of respect so the Challah not be discarded as regular trash. [See Hakashrus ibid] Others however make no mention of this requirement and as long as it is wrapped once it suffices. [Piskeiy Teshuvos ibid]
 See Koveitz Mibeiys Leivi 3 p. 22; Avnei Yishpeh 3/72; Hakashrus ibid