Thanks Jeff,It is very possible that the big chrome escutcheon over the cartridge can be unscrewed counter clockwise, which will expose the cartridge.
You can try grabbing it hard with just your hands.
You might need a strap wrench, which grabs without scratching.
They are often stuck on tight, and if so sometimes you can tightly wrap four or five layers of duct tape around the escutcheon and grab it with a pair of channel lock pliers.
You can also get pliers with rubber covers that go over the jaws, so they are less likely to dig into the chrome.
Then you might have to unscrew a large nut which holds the valve body tight to the countertop, and then the valve can be removed from below.
Or if you are lucky, once you remove the escutcheon, sometimes the cartridge can just be removed from above.
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