Melt butter in a large pot over medium heat.

Add onion, garlic, and thyme and sauté until onion has softened, about 5 minutes.

Add squash and chicken broth; bring to a simmer, then cook until squash is tender, 10 to 15 minutes. Crumble bouillon into the soup. Season with cumin, allspice, salt, and pepper, then remove from heat.

Working in batches, pour soup into a blender, filling no more than halfway.

Hold the lid in place with a kitchen towel, then carefully start the blender using a few quick pulses to get the soup moving before leaving it on to purée.

Pour soup into a serving bowl. Alternately, you can use a stick blender and purée the soup in the pot.