You can make the boozy fruit puree up to two days in advance. Top with seltzer and garnish with blackberries, lime wedges, and marjoram leaves before serving. Recipe courtesy of Erin French, chef and owner of Lost Kitchen in Freedom, ME.
Puree blackberries, lime juice, vodka, sugar, and marjoram in a blender. Strain through a fine-mesh sieve, pressing on solids with a flexible spatula; discard solids. Puree can be made ahead and refrigerated in an airtight container up to 2 days.
Divide puree among 8 ice-filled glasses. Fill with seltzer; stir. Serve, garnished with blackberries, lime wedges, and marjoram.