Cut kernels from corncobs; place in a bowl. Using the large holes of a box grater, scrape liquid and pulp from cobs into another bowl. Discard cobs.

Melt butter in a medium saucepan over medium-high. Add onion, and cook, stirring often, until tender, about 4 minutes. Stir in corn kernels, garlic, salt, and pepper; cook, stirring occasionally, 3 minutes. Add water and reserved corn liquid and pulp. Bring to a boil over medium-high. Reduce heat to medium-low, and simmer 4 minutes. Transfer to a blender, and add olive oil. Remove center piece of blender lid (to let steam escape); secure lid on blender, and place a clean towel over opening in lid. Process until smooth, 2 minutes.

Pour mixture through a fine wire-mesh strainer into a bowl; press with the back of a spoon to extract as much liquid as possible. Discard solids. Stir in vinegar; cover and chill 4 to 8 hours. Pour into 6 (4-ounce) glasses; add toppings.