In a small saucepan, combine the fresh blackberries with ½ cup of cold water. Place the saucepan over medium heat, and using a fork, gently mash the blackberries as they cook. Continue cooking for about 5-7 minutes until the blackberries are soft and begin to release their juices.
Once cooked, remove the saucepan from heat. Strain the blackberry mixture through a fine mesh sieve into a bowl, using a spatula or the back of a spoon to press down and extract as much juice as possible. Discard any seeds and pulp left behind. Set the vibrant blackberry syrup aside.
Using the same saucepan, add another ½ cup of water and introduce the fresh sage leaves. Simmer gently over low heat for about 5 minutes to allow the sage to infuse its flavor into the water. Afterward, remove from heat and let the sage steep for an additional 10 minutes. Strain the sage leaves out, discarding them.
In a large pitcher, combine the prepared blackberry syrup, sage-infused water, freshly squeezed lemon juice, sugar, and the remaining 3 cups of cold water. Stir thoroughly until the sugar is completely dissolved. Taste the mixture and adjust sweetness if needed, by adding more sugar or water to your preference.
Cover the pitcher and refrigerate the lemonade for at least 30 minutes. This chilling time allows the flavors to mingle beautifully.
To serve, fill glasses with ice cubes and pour the chilled lemonade over the top. Garnish each glass with fresh lemon slices and a sprig of sage for a delightful touch.
Notes
Adjust sweetness to taste and serve chilled for the best flavor.