The rule
canon's timing law
Chill first, roll second
A cold, firm dough ball takes a thick even coat that stays on the outside where it can work.
Roll a room-temperature ball and the sugar starts dissolving on contact, sinking into the dough as a sweetener rather than sitting on it as a crust. The cookie comes out sweeter and plainer-looking, which is precisely the trade nobody wanted. If the dough has warmed up while you shaped it, put the balls back in the fridge for ten minutes before they meet the bowl.
What it does
The coat is what makes the top crackle
Sugar on the surface dries the exterior as the cookie bakes, setting it early while the inside is still rising.
That mismatch is what cracks the top, and a fine, even crackle is the marker the literature uses for a well-made cookie in this family. It is the same mechanism that gives a snickerdoodle its surface, which is why a cinnamon-sugar roll on a sugar cookie reads as a cousin rather than a new idea. One cook in our reviews made exactly that swap and described the result as a snickerdoodle, which is the honest name for it.
Choose your sugar
Granulated crackles, sanding softens
The size of the crystal decides whether you get a crust or a decoration.
Cooks who used coarse sanding sugar reported deliberately soft, underdeveloped edges: the big crystals sit on top and sparkle rather than drying the surface. Powdered sugar on the work surface simply read sweeter. Ordinary granulated is what does the technical job. Sprinkles rolled on after a short chill went down well and are doing an appearance job, not a texture one.