Step 1

Combine apple, garlic, bread, grapes, blanched almonds, milk, and 2 cups water in a medium bowl; season with salt. Cover and chill for at least 6 hours and up to 1 day.

Step 2

Transfer soup base to a blender and purée, adding water by tablespoonfuls if too thick, until smooth. With motor running, gradually add ¾ cup oil and 3 Tbsp. vinegar and blend until soup is emulsified. Season with salt, pepper, and more vinegar, if desired. Strain soup through a fine-mesh sieve into a large bowl; cover and chill until very cold, about 2 hours.

Step 3

DO AHEAD: Soup can be made 1 day ahead. Keep chilled.

Step 4

Preheat oven to 350°. Spread sliced almonds on a rimmed baking sheet and toast, tossing occasionally, until golden, about 4 minutes. Let cool.

Step 5

Divide soup among bowls. Top with toasted almonds; drizzle with oil and vinegar.