Combine cauliflower florets, smashed garlic, and vegetable broth in a large pot. Bring to a boil over high heat, then reduce to a simmer and cook until the cauliflower is completely tender and easily pierced with a knife, about 15 minutes. The cauliflower should almost fall apart when poked.

Using a slotted spoon, transfer the cooked cauliflower and garlic to a high-speed blender. Add 1 cup of the cooking liquid, the butter, heavy cream, Parmesan, salt, pepper, and nutmeg. Blend on high until completely smooth and silky, 1 to 2 minutes, scraping down the sides as needed. If the sauce is too thick, add more cooking liquid a few tablespoons at a time.

Taste the sauce and adjust seasoning with more salt if needed. Add the lemon juice and pulse once more to combine. The sauce should coat the back of a spoon and taste rich and slightly nutty from the Parmesan.

Serve immediately over pasta, roasted vegetables, or grilled chicken. Top with additional grated Parmesan and freshly cracked black pepper.