Make the blackberry-vanilla syrup: In a small saucepan, combine blackberries, sugar, and water. Bring to a gentle simmer over medium heat, stirring and mashing the berries lightly with a spoon. Cook 6–8 minutes until the berries soften and the liquid turns deep purple.

Add vanilla: Remove from heat. Stir in vanilla extract (or split vanilla bean added during simmering). For extra winter warmth, add a tiny pinch of cardamom or a strip of orange zest, then fish it out before straining.

Strain: Press the mixture through a fine mesh strainer into a jar. Discard seeds and pulp. Let the syrup cool completely. You should have about 3/4 cup.

Prep your glass: Fill a tall glass with ice. Add 1.5–2 ounces (3–4 tablespoons) of the syrup, depending on sweetness preference.

Add citrus: Squeeze in 1–2 teaspoons of fresh lemon juice for brightness.

Top with bubbles: Slowly pour in 4–6 ounces of very cold sparkling water or club soda. Stir gently once to combine and keep the fizz.

Garnish and serve: Add a couple of fresh blackberries and a rosemary sprig. Serve immediately while frosty and effervescent.