A Larabar is a date bar, and while there are multiple varieties, dates are the primary ingredient.
Although dates, when pressed into a dough, are not readily identifiable, at least visually, as dates, Shulchan Aruch (O.C. 202:7, and cited in Mishna Berurah, 202:42) nevertheless states that the appropriate bracha is Borei pri haetz (in many other cases, when a fruit, or food, loses its identity and is subsumed in a mass or dough, the appropriate bracha is shehakol (See Mishna Berura 202:42).
One must eat a minimum of a kezayis of the date itself or in combination with other fruits of the shivas haminim (grapes, figs, olives, pomegranates) in order to make an “al ha’etz”. The size of a Larabar is 2.8 inches long, 1.3 inches wide, and .56 inches thick. This means that it is just over two cubic inches, or about 34 cubic centimeters (or 1.1 fluid ounces). According to Rav Chaim Nah, a kezayis is 27 cubic centimeters.
Therefore, even in a bar which contains 70 percent date, there is only about 23 cubic centimeters of dates. Even if the bar contains some raisins it is unlikely that there would be a kezayis of shivas haminim fruit. Therefore, an “al haetz” would be inappropriate after eating only one Larabar.
However, two Larabars definitely contain a kezayis of dates – even if dates were to make up only 40 percent of the bar and the bar contains no raisins.
After eating only one Larabar, the appropriate beracha is borei nefashos (see Mishna Berura 210:1). After eating two bars, the appropriate bracha is al haetz.
There may or may not be a kezayis of date after one and a half Larabars, and therefore unless one can tell that there is clearly a kezayis of dates and possibly raisins, the safest strategy is to either eat no more than one bar or to make sure to purchase at least two bars.
Blessed are You Hashem our God king of the universe, Who creates the fruit of the trees.
Baruch Atah Adonai, Eloheinu Melech Haolam Borei Pri Haetz.
Blessed are You, Hashem our God, King of the universe, for the tree and the fruit of the tree, for the produce of the field, and for the precious, good, and spacious land which You have graciously given as a heritage to our forefathers, to eat of its fruit and to be satiated with it’s goodness. Have mercy, Hashem our God, on Israel Your people, on Yerushalayim Your city, on Zion the resting place of Your glory, on Your altar, and on Your Temple. Rebuild Yerushalayim, the holy city, speedily in our days, and bring us up to it and make us rejoice in it, and we will bless You in holiness and purity. For You, Hashem, are good and do good to all, and we offer thanks to You for the land and for the fruits. Blessed are You, Hashem, for the land and for the fruits.
Blessed are You, Hashem our God, King of the universe, Who creates numerous living things with their deficiencies; for all that You have created with which to maintain the life of every being. Blessed is He, the life of the worlds.
Baruch Atah Adonai, Eloheinu Melech Haolam, Al Haetz V’al Pri Haetz, V’al Tnuvas Hasadeh, V’al Eretz Chemda Tova Ur’chava, Sheratzisa V’hinchalta Lavoseinu, Le’echol Mi’pirya V’lisbo’a Mituva. Racheim Adonai Eloheinu Al Yisrael Amecha, V’al Yerushalayim Irecha, V’al Tzion Mishkan K’vodecha, V’al Miz’b’checha V’al Heichal’echa. U’v’nay Yerushalayim Ir Hakodesh Bim’hayra V’yameinu, V’ha’aleinu L’socha, V’samcheinu B’vinyana, V’nochal Mipirya, V’nisba Mituva, Oonevarech’cha Aleh’ha Bikdusha Oov’tahara. Ki Atah Adonai Tov U’maitiv Lakol, V’nodeh Lecha Al Ha’aretz V’al Hapeiros. Baruch Atah Adonai, Al Ha’aretz V’al Hapeiros.
Baruch Atah Adonai Eloheinu Melech Haolam, Borei Nefashos Rabos V'chesronan Al Kol Ma Shebarasa L'hachayos Bahem Nefesh Kol Chai, Baruch Chei Haolamim.