Preheat oven to 425°. Grease a large rimmed baking sheet. Remove husks and silks from corn. Cut kernels from corn cobs over a large bowl; reserve cobs. Spread corn in even layer on baking sheet. Bake until roasted and golden around the edges, 25 minutes, stirring halfway during the cooking.
Meanwhile, place corn cobs in large pot and add 8 cups water. Bring to simmer and cook covered until water is corn-flavored, about 45 minutes. Remove cobs and discard.
Reserve 1/2 cup roasted corn for relish. Working in batches, place one third of remaining corn in blender. Add 1 1/3 cups corn liquid; cover and carefully blend until smooth. Place in strainer set over a large bowl. Strain; discard solids. Repeat with remaining corn and liquid. Stir buttermilk, salt, pepper and 1 cup corn liquid into bowl. Cover and refrigerate until well chilled, 2 hours.
In medium bowl, toss together tomato, vinegar, oil, thyme and reserved 1/2 cup corn to combine. Ladle chilled soup into bowls and top each with 2 tablespoons tomato mixture.More recipes from Blackberry Farm: