Tomorrow (beginning from tonight) marks Rosh Chodesh Shevat. Tu Bishvat, a day we customarily recite many blessings, falls out during this month. We shall therefore discuss the laws of blessing during the next several days.
The Mishnah in Masechet Berachot (44a) states: “The rule is: If there is a primary food and a secondary food along with it, one recites a blessing on the primary food and exempts the secondary food.” This means that when two kinds of food are mixed together, one recites a blessing on the primary food and exempts the secondary kind. For example, if one has a dish of rice with some beans on top of it, the rice is considered primary and thus, one recites a “Boreh Minei Mezonot” blessing on it and this is sufficient to exempt the blessing on the beans as well.
This law regarding primary and secondary foods is true not only regarding two foods mixed together, such as the example of rice and beans; the same applies if one eats the secondary food alone, for instance, if one recited a “Boreh Minei Mezonot” blessing and eats some rice and then wishes to eat some beans alone, without any rice, one would still not recite a blessing on the beans, for it is nevertheless secondary to the rice and has already been exempted by its blessing.
It is for this reason that one does not recite a blessing on the jelly-filling of a donut, even if one wishes to eat it on its own. Similarly, one should not recite a blessing on the cheese-filling of a cake, even if one wishes to eat it on its own, for in these cases as well, the primary food exempts the secondary one.
Maran Rabbeinu Ovadia Yosef zt”l writes that if one recites a “Boreh Minei Mezonot” blessing and eats cake and then wishes to drink tea or coffee along with the cake, the tea or coffee is not considered secondary to the cake and therefore exempted by its blessing; rather, one must recite the “Shehakol” blessing on the tea or coffee, after which one may dip the cake into the tea or coffee as one wishes.
Similarly, if one drinks water or juice while eating cake or a dish upon which the “Mezonot” blessing is recited, one must recite the “Shehakol Nihya Bidvaro” blessing on the beverage; if one drinks a Revi’it (approximately 2.7 fluid ounces) of the beverage in one shot, one must likewise recite the “Boreh Nefashot” blessing after concluding to drink.