In a medium pot, melt the 3 tablespoons butter over over medium-high heat. Add the onions, salt, pepper, and nutmeg and cook, stirring, until opaque, 4 minutes. Add the garlic and thyme, stirring until fragrant, for 20 seconds. Add the flour and cook, stirring until flour is absorbed, try not to burn the flour. You can add a smidgen more butter when the flour gets real brown, if needed. Slowly add the chicken stock, whisking constantly, and bring to a boil. Reduce the heat and simmer until thickened, about 3 minutes. Add the broccoli and cook, stirring, until tender, about 10 minutes.

Remove the pot from the heat and puree with a hand-held immersion blender until loved. I like chunky soup, so I blend on low for 3 minutes. If you like a very creamy soup, blend on high for 5 minutes.

Add the cream and bring to a bare simmer to heat through. Add most of the cheese, reserving an eighth for garnish, and cook over low heat, stirring until melted. Add the 2 tablespoons cold butter, stirring to blend.

Remove from the heat and ladle into bowls. Sprinkle croutons over the top of the soup and serve immediately.