What Blessing Do We Say on Marshmallow?

For themarshmallow, we recite Shehakol (the first blessing).

And after eating, recite Borei Nefashot (the final blessing).

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Required consumption amount for the final blessing (from "Halacha Yomit" based on rulings by Maran Rabbi Ovadia Yosef, of blessed memory):

For any food that a person eats, they should say a "first blessing," such as the blessing "Shehakol" or "Ha'etz." Even if consuming only a small amount, one must bless as long as it is being eaten intentionally. (However, if only tasting to adjust seasoning, no blessing is required.) Therefore, someone chewing flavored gum, even if swallowing very little, must bless for deriving pleasure from its flavor. Similarly, if drinking something, one should bless even if only taking a single drop.

However, all this applies only to the first blessing, but a final blessing is recited only after a "significant consumption." The measure of significant consumption is a volume of "kezayit," which is twenty-seven grams, and for drinks, the measure is "revi'it," which is eighty-one grams.

Additionally, the eating or drinking must occur within a time frame where these consumptions are considered combined. For instance, if a person eats a "kezayit" of bread over an entire day, piece by piece, they certainly cannot recite Birkat Hamazon. Rather, the "kezayit" must be consumed within the time frame of "eating a pras," with varying opinions on this duration, some say five minutes, others seven and a half minutes (and there are additional views). Therefore, it is advisable to always consume a kezayit (especially during Shabbat meals) within four and a half minutes to satisfy all opinions.

Regarding the final blessing on drinks, one must drink a revi'it (eighty-one grams) at once; if there is a pause between sips, no final blessing is recited. Therefore, sipping soup from a spoon does not warrant a final blessing, nor does slowly drinking hot coffee or tea, since they cannot be consumed in one go.