In a large jar, combine coarsely ground coffee and cold water in a 1:4 ratio. Stir well, cover tightly, and let it steep in the refrigerator for at least 12 hours.

In two glasses, add fresh blackberries, a few sage leaves, and maple syrup. Muddle gently to release juices and flavors.

Strain the cold brew concentrate through a coffee filter or fine mesh strainer to separate liquid from grounds.

Fill each glass with ice cubes and pour the strained cold brew over the muddled mixture.

Warm the barista oat milk over low heat, whisk in more maple syrup, then froth until smooth.

Dollop the frothy oat milk on top of each glass, garnish with fresh sage leaves and blackberries.