1. Melt butter in a Dutch oven over medium-low heat. Add onion to pan; cover and cook 10 minutes or until tender, stirring occasionally. Add corn and next 4 ingredients (through pepper); bring to a boil. Reduce heat, and simmer 15 minutes. Cool slightly. Place half of corn mixture in a blender. Remove center piece of blender lid (to allow steam to escape); secure blender lid on blender. Place a clean towel over opening in blender lid (to avoid splatters). Blend until smooth. Strain corn mixture through a sieve into a large bowl; discard solids. Repeat procedure with remaining corn mixture. Garnish with squash blossom slices, if desired.