准备

• Purée the blackberries with 1/2 cup water and the lemon juice in a blender until completely smooth. Strain through a fine-mesh sieve set over a large bowl. Rinse the blender and sieve. Refrigerate the purée until very cold, about 30 minutes. (You can refrigerate the purée up to 1 day).
• 将糖和1杯水放入中等的容器中。紧紧盖住并摇动直到糖溶解。加入玉米糖浆；搅拌以结合。在冰箱中冷却直到冷约30分钟。
• Put the blackberry purée, 1 cup of the simple syrup, the elderflower liqueur, and guar gum (if using) in a blender. Blend until smooth. Strain the mixture through a fine-mesh sieve into a tall (6 to 8 cup) container.
• To check the density of the sorbet base, gently lower the egg into the container with a slotted spoon (don’t drop it in or it could break). If the egg sinks, remove it and stir in 2 Tbs. of the simple syrup. The goal is to adjust the sugar density with the syrup until the egg floats just below the surface of the sorbet base with an exposed area of shell that’s about the size of a quarter. Keep testing with the egg, adding more syrup 2 Tbs. at a time, until the egg floats as shown below. When it does, remove the egg. Refrigerate the sorbet base until very cold, at least 30 minutes.
• Freeze the sorbet base in an ice cream maker according to the manufacturer’s instructions. While the sorbet is churning, put two pint-size containers in the freezer. Transfer the sorbet to the pint containers and freeze until hardened, at least 4 hours. If the sorbet hardens too much to scoop, let it sit in the refrigerator for 20 minutes before serving.

Make Ahead Tips

You can make the syrup up to 2 weeks ahead and store, covered, in the refrigerator.

You can refrigerate the sorbet base for up to 1 day before freezing.

成品冰糕将在冰箱中持续2周；之后，质地可能会变得冰冷，但是您可以解冻并重新冻结冰淇淋制造商中的基础。