Peel the beet and slice it as thinly as possible using a mandolin or a vegetable peeler.
Mix the sugar and ground coriander together in a small bowl.
Place a couple layers of kitchen paper on a microwave-safe dish. Arrange the beet slices on top of the kitchen paper without overlapping. Microwave on high for 3 minutes, until the slices are wrinkled and crisp.
Transfer to a serving dish and immediately sprinkle a little of the spiced sugar mix over the warm crisps. Repeat until all the slices are cooked.