Of all the kitchen gifts I've received, the one I use most is my ice cream maker. The Gaggia gelatiera, bought in Italy by my husband, has a built-in freezer unit so it churns and freezes at the same time.
As with all desserts, the frozen variety needs to be balanced in taste and texture, and isn't - or shouldn't be - as hard as ice. The proportion of ingredients plays a role in ensuring it's scoopable and pleasant to eat, even when taken straight from the freezer. But also important is the amount of air ('overrun') incorporated during the freezing process: too much and the flavour will be less intense; too little and the finished product will be too hard.
Frozen desserts can be placed into two broad categories: those with and those without fat. Water ices - such as sorbet and granita - are made with just sugar, water and another liquid, such as fruit puree, coffee, tea or wine. Ice cream and gelato (to name just two) contain fat, which can come in the form of egg yolks and/or dairy products, such as cream, milk or cheese.
Sugar is used in all types of frozen desserts. It doesn't just provide sweetness, it's also important for texture: sugar makes it smooth and prevents it from freezing too hard. Use too much and the dessert will feel coarse on the tongue (which is fine if it's a granita); use too little and the food will be too soft.
When making sorbet, I use a formula that suits almost all types of fruit puree. Make a sugar syrup by dissolving two parts sugar into three parts water (by weight), then use the same proportion when mixing the syrup with strained fruit puree, respectively. Add fresh lemon or lime juice and a splash of vodka (or another type of alcohol that complements the fruit, such as rum with pineapple). Sometimes I add a tiny amount of egg white.
The lemon or lime juice balances the sugar in the fruit and syrup. Without it, the sorbet will be too sweet. Because alcohol doesn't freeze, it's added to frozen desserts (not just sorbet) to prevent them freezing too hard. Lightly whisked egg white makes the texture lighter.
The richest ice creams have a custard base: egg yolks with cream and milk, in addition to the sugar and other flavorings. This works best for flavours such as vanilla, chocolate and any type of nut. However, when making chocolate or nut ice cream, take the additional fat content of those ingredients into consideration. If you add chopped chocolate to a standard custard base, the ice cream would be too rich and also very soft, because fat doesn't freeze solid.
I rarely use a custard base in fruit ice cream, because the richness obliterates the delicacy of the fruit. Instead, I chop a small amount of fruit and macerate it with granulated sugar and some alcohol (if you skip this step, the chunks of fruit will freeze too hard). Puree the rest of the fruit with more sugar, mix in double cream and a shot of alcohol, then freeze in the ice cream maker. When it's ready, fold the chopped fruit into the ice cream, pack into a container and freeze for several hours. This firms it up (it's too soft straight out of the machine) and lets the flavours blossom.