3 tablespoons unsalted butter, plus 2 tablespoons cold unsalted butter, cut into pieces
1 cup yellow onions or sliced leeks (white parts only, well rinsed)
1/2 teaspoon salt
1/4 teaspoon freshly ground white pepper
1/2 teaspoon minced garlic
1/2 teaspoon chopped fresh thyme leaves
3 tablespoons all-purpose flour
3 cups pareve chicken stock
1 (16-ounce) package frozen broccoli, thawed and separated
1/2 cup heavy cream, milk or soymilk
1-1/4 cups shredded medium Cheddar
Croutons for garnish (for Passover use toasted matza as a garnish)
In a medium pot, melt the 3 tablespoons butter over medium-high heat. Add the onions, salt, pepper, and nutmeg and cook, stirring, until soft, 3 minutes. Add the garlic and thyme cook, stirring, until fragrant, for 20 seconds. Add the flour and cook, stirring until the mixture is well blended and smells fragrant, 2 minutes. Slowly add the pareve chicken stock, whisking constantly, and bring to a boil. Reduce the heat and simmer until thickened, about 5 minutes. Add the broccoli and cook, stirring, until tender, for 10 minutes.
Remove the pot from the heat and puree with a hand-held immersion blender. (Alternatively, in batches, puree in a blender or food processor and return to the pot.)
Add the cream and bring to bare simmer to heat through. Add the cheese and cook over low heat, stirring, until melted. Add the remaining 2 tablespoons cold butter, stirring to blend.
Remove from the heat and ladle the soup into bowls. Sprinkle croutons over the top of the soup and serve immediately.