Step 1: In the bottom of a cocktail shaker or a sturdy glass, combine the fresh berries (about 1/4 cup per serving) and 5-6 fresh mint leaves. Add 1/2 ounce of simple syrup.
Step 2: Gently muddle the berries and mint. The goal is to release the juices from the berries and the oils from the mint, not to pulverize them into a pulp. About 5-7 presses should be enough.
Step 3: Add 1/2 ounce of fresh lime juice to the muddled mixture.
Step 4: Fill the shaker or glass with ice. If using a shaker, cap it and shake vigorously for about 15-20 seconds until the mixture is well-chilled. If using a glass, stir well with a spoon.
Step 5: Strain the mixture into a tall glass filled with fresh ice. You can use a fine-mesh strainer to ensure no berry pulp or mint pieces get through, or if you prefer a bit of texture, pour directly.
Step 6: Top the glass with about 4-6 ounces of cold sparkling water or club soda. Stir gently to combine the layers.
Step 7: Garnish with a few fresh berries, a lime slice, and a sprig of fresh mint. Serve immediately and enjoy!