Begin by placing the fresh blackberries in a medium mixing bowl. Using a fork, gently mash the blackberries until they are mostly broken down, retaining some texture for added depth.
Once mashed, incorporate the fresh thyme leaves and honey (or agave syrup) into the blackberry mixture. Stir well to ensure everything is evenly mixed. Allow this mixture to rest for approximately 5 minutes.
After the resting period, strain the blackberry mixture through a fine mesh sieve into a pitcher. Use the back of a spoon to press down on the mixture, extracting as much delicious juice as possible.
Introduce the freshly squeezed lemon juice to the strained blackberry syrup. Stir gently until the syrup is fully combined.
Prepare your serving glasses by filling each with ice cubes. Pour about 1/4 of the blackberry syrup into each glass, adjusting the amount based on your sweetness preference.
Carefully top each glass with sparkling water. Use a spoon to gently mix the drink, ensuring the syrup and water blend seamlessly together.
For an elegant finishing touch, garnish each mocktail with a sprig of thyme and, if desired, add a slice of lemon to the rim of the glass.
Notes
Serve in clear glasses to showcase the vibrant color and texture.