When the asparagus is cool enough to handle, trim off the tips; save these pieces for garnish, if you wish; add the remaining asparagus pieces to a food processor and blend until very smooth (purée).
Melt butter in a stock pot over medium heat; add the onion and cook until it begins to soften, ~4 minutes.
Add garlic and cook until fragrant, ~30 seconds more; sprinkle in the flour, salt, pepper and coriander; stir to combine.
Slowly whisk in the cream and broth until smooth; bring to a bubbly boil; reduce heat to low and simmer, stirring occasionally, until the mixture starts to thicken, ~15 minutes.
Stir in the asparagus purée; let the soup heat through.