Step 1

In a medium pot, melt butter over medium. Add onion and cook, stirring occasionally, until softened, 8 minutes.

Step 2

Add flour and cook, stirring, until combined, 1 minute.

Step 3

Whisking constantly, add broth and 1 cup water and bring to a boil over high. Reduce heat and simmer, whisking occasionally, 10 minutes.

Step 4

Add broccoli and bring to a simmer. Cook until broccoli is very tender, 20 minutes.

Step 5

Transfer mixture to a large bowl. In batches, fill a blender halfway with mixture and puree until smooth; to allow heat to escape, remove cap from hole in lid, cover lid with a dish towel, and hold down firmly while blending. Return soup to pot as pureed.

Step 6

Add cream and heat over medium until warmed through. Season with salt and pepper. Thin with broth or water, if desired.