Add water, tea bags, and a half cup blackberries to Instant Pot® and stir to combine. Add lid and lock into place. Switch the vent to “Sealing” and set the “Manual” setting to 5 minutes.
While the tea is brewing, add remaining blackberries, basil, sugar substitute, and water to saucepan set over medium heat. Cook, gently pressing on the blackberries to release their juices while continually stirring the mixture to combine, for 4-5 minutes.
When cook time on Instant Pot® is complete, allow pressure to release naturally for 10 minutes, then do a quick release to release any remaining pressure.
Carefully strain hot tea mixture with a fine mesh strainer. Pour the reserved liquid into a large, heat-resistant pitcher and sweeten with the blackberry simple syrup, to taste. Add fresh lemon juice and stir to combine.
Serve immediately over ice with fresh blackberries and a sprig of fresh basil for garnish. Enjoy!
Notes
To reduce bitterness, add a pinch of baking soda prior to brewing and remove tea bags as soon as the pressure has been fully released.