In a Dutch oven, heat oil over medium-high heat. Add onion; cook until translucent, approximately 5 minutes. Add garlic; cook for 1 minute. Add carrot and celery, stirring to combine; cook for 5 minutes. Add squash, broth, thyme, salt, and curry powder. Bring mixture to a boil. Reduce heat to low, and let simmer until vegetables are tender, approximately 25 minutes.
Remove and discard tied thyme. Let cool slightly. Using a stick blender, purée soup until smooth.
Garnish individual servings with thyme leaves, if desired.
Notes
Make-Ahead Tip: Soup can be made up to 2 days in advance, stored in an airtight container, and refrigerated. Warm soup over medium-low heat before serving.
Recipe by TeaTime Magazine at https://teatimemagazine.com/acorn-squash-soup/