From Cooking Light magazine, via MyRecipes.com (see Links), this summer cooler is great to enjoy as the last summer days turn to autumn. Recipe may be halved.
6 cups water
3 cups fresh blackberries
1 cup sugar
2/3 cup fresh lime juice (about 4-6 limes)
lime slices, for garnish
Place 1 cup water and 3 cups blackberries in a blender and process until smooth. Press blackberry puree through a sieve into a large pitcher and discard seeds. Add remaining 5 cups water, sugar, and lime juice to pitcher. Stir well to dissolve sugar. Serve over ice and garnish with a lime slice.
The blackberries used below came from a local Farmer’s Market:


