I thought that mud cracks and the crazing one sees in ceramics is governed by the microscopic character of the mud / clay and so will not scale up. But maybe it does.
Here are giant cracks on a dry lake bed on Mars. Same processes at work as on earth.
But still 3 orders of magnitude less than what you want.
I was not able to find cracks this big on earth. I thought maybe the Aral Sea but no. I think maybe the big ones on Mars are an artifact of Martian conditions. You could handwave up what those are and magnify them but I worry about your inhabitants - a difference between Mars and Earth but 100 times more starts getting iffy.
There is a different way to make big cracks that result in adjacent irregular polygons. Ice.
These shapes are made by the pressures of the ocean beneath. The ice is relatively thin. But what if the ice were phenomenally thick, covering the planet and the pressures from beneath were immense? Could you crack an ice layer kilometers thick into the giant blocks and crazed patterns you want?
Europa's icy surface is covered with immense cracks many kilometers long. Maybe it is not tessellated enough for your purposes but you could make it more so. The topic of these cracks was addressed on the planetary science stack.
Stolen from that answer:
The exact nature behind formation of these younger cracks is still
somewhat of a mystery, but most of the theories suggest a combination
of interactions between Europa and Jupiter, such as tidal forces,
effects of changes in strength of Jupiter's magnetosphere as the
satellite orbits it, Jupiter as a source of radiation causing
greenhouse effect on Europa's liquid subsurface with the surface
isolating the heat within its shroud, and also difference in radial
velocity of the liquid oceans compared to its surface and possible
geological activity beneath them to keep this oceanic mass warm enough
to remain liquid, forming surface cracks similar to those found in the
polar regions on the Earth, and perhaps even warm enough at its bottom
to sustain some forms of life.
Europa is still cracking. I think your planet will have to still be cracking too: the flexing produced by Jupiter is not something one can easily turn off.
I wonder if you had a smooth siliceous lava flow (maybe from an ancient impact?) covering the surface of a planetary body if it could be cracked in a similar way, by immense tidal forces flexing it?