Dry sauté the onion in a small pot over medium heat, stirring constantly, until browned, 4–5 minutes.
Add the flour and cook, stirring constantly, for 30 seconds.
Add the broth, cashews, and garlic and bring to a simmer.
Cook for 10 minutes.
Transfer to a blender and process on high speed until smooth.
Serve warm, chilled, or at room temperature.