The gemara[1] presents the basic rules of berachot during a meal in which one ate bread. Foods that “come due to the meal” do not require a beracha, whereas those foods that are not due to the meal require a beracha before eating them.
The Rosh[2] describes foods that come due to the meal as those that are connected to the main part of the meal and are usually eaten with bread. Fruits are prime examples of foods that are not due to the meal.[3] They are ordinarily eaten to impart a sweet taste, rather than to satiate. Poskim further assume that foods brought to the table relatively close to Birkat HaMazon are eaten specifically for dessert and generally do not come due to the meal,[4] which makes them candidates for a beracha. However, because of certain factors, some of which we will discuss, it may not always be necessary to recite a beracha before eating them.
The gemara[5] asks why, according to these rules, one is required to make a beracha on wine drunk during the meal. Wine appears to be part of the meal, and therefore should not have its own beracha. The gemara answers: “Wine is different, as it causes a beracha for itself.” The most accepted explanation is that wine is unique in that we make a beracha on it in various mitzva contexts (e.g., Kiddush and Sheva Berachot), even when we are not interested in drinking it.[6] It follows that were it not for this unique characteristic, wine would indeed not have required a beracha during a meal. Accordingly, most Rishonim and the Shulchan Aruch[7] posit that other drinks consumed during the meal, even toward its end, do not require a beracha. Many explain that eating contributes to one’s thirst, and quenching thirst is thus an integral part of the meal.
We should note that some Rishonim understand the gemara differently and argue that one makes a beracha on all drinks during the meal. The Shulchan Aruch[8] even cites this view as a minority opinion and suggests removing doubt by making a Shehakol before the meal to cover drinks. However, this is certainly not the standard practice.
Surprisingly, the idea of berachot on drinks is crucial for your question about ice cream. At first glance, ice cream is a classic dessert, meant to finish the meal with a sweet taste. Unlike drinks, it is neither present during the main meal nor is it intended to quench one’s thirst. Nevertheless, a number of poskim claim that ice cream is really a liquid; it is served as a solid because people enjoy it at a very cold temperature. These authorities argue that since the accepted practice is to not make a beracha on liquids during a meal, including during dessert, one should not make a beracha on ice cream. Rav Moshe Feinstein is cited as maintaining that one does not make a beracha on ice cream for dessert.[9] Yalkut Yosef[10] also rules this way in the name of his father, Rav Ovadia Yosef, who also points out that ice cream is not chewed like foods. Some distinguish between ice cream whose main ingredient is milk, making it a frozen liquid, and ice cream that is a mixture of eggs, soy products, and sugar (i.e., most pareve ice cream).[11] Perhaps Rav Moshe was speaking only about classic ice cream. However, Rav Ovadia does not accept this distinction.
It is difficult, on fundamental grounds, to accept the above ruling (despite the principle of safek berachot l’hakel, which would indicate that we should not say a beracha in a situation of doubt). The great majority of poskim understand that the matter does not depend on the halachic definitions of liquid vs. solid, but rather on the function of the food. Drinks that relate to the essential meal do not necessitate an additional beracha; foods eaten as dessert do. (The reason that we do not make a beracha on most cakes eaten for dessert is that they may have a halachic status of bread.[12]) Even among drinks per se, the Mishna Berura[13] mentions some situations and opinions about a beracha for whiskey or coffee at the end of a meal, and the main determinant is its function vis-à-vis the meal. Indeed, the gemara did not state a formal rule about liquids during a meal. There is thus little reason to lump together all liquids, and especially not ice cream, when their roles in the meal are so different.
Most poskim rule that one should make a beracha on ice cream. Some suggest avoiding the issue by first making a beracha on a food that all agree requires Shehakol (e.g., candy).[14] We recommend making a beracha on ice cream served as a dessert unless one always follows Rav Moshe’s or Rav Ovadia’s rulings.