The syrup must be cool to the touch before the berries go in. Warm syrup bursts the skins and the whole batch turns to mush.
Sort ruthlessly. Any berry with a split, soft spot or wrinkle will leak and dissolve its coating. Firm berries squeak when you press them.
For the North American sparkling style, roll in coarse sanding sugar instead of powdered sugar. You get crunch and glitter rather than a matte snow finish.
Traditional Soviet factories used lightly whisked egg white as the binder instead of syrup. If you want that version, whisk one egg white until just frothy, toss the berries in it, drain, then dust.
Serve loose in a candy dish with hot spiced black tea, scatter them over a pavlova or cheesecake, or perch a few on a cheese board. They also make a fine cocktail garnish.
These are not shelf stable. They keep 2 to 3 days uncovered or loosely covered at cool room temperature. Never refrigerate or freeze them, the coating will dissolve into syrup.
Frozen cranberries work but weep as they thaw, giving a wetter, duller shell.