For the blackberry mixture

• 500 g fresh ripe blackberries (about 4 cups)
• 500 ml whole milk (2 cups)
• 180 g granulated sugar (¾ cup plus 2 tablespoons)
• 5 ml vanilla extract (1 teaspoon)
• 1 g ground cinnamon (½ teaspoon)
• 15 ml fresh lemon juice (1 tablespoon)

For the ice bed

• 3 kg crushed ice
• 900 g coarse salt or sea salt
• 500 ml cold water (2 cups), only if needed to pack the ice bed