Prep the produce: Hull and slice 2 cups of strawberries. Chop 2 cups of rhubarb into 1/2-inch pieces. Measure 1 cup sugar and 1 cup water.
Make the syrup: Add strawberries, rhubarb, sugar, and water to a saucepan.
Bring to a gentle simmer over medium heat, stirring occasionally.
Simmer until soft: Cook for 12–15 minutes, or until the fruit breaks down and the liquid turns rosy and fragrant. Avoid a hard boil to prevent scorching.
Add lemon: Stir in 1–2 tablespoons fresh lemon juice to brighten the flavor. Taste and adjust sweetness if needed.
Strain: Place a fine-mesh sieve over a bowl or measuring cup.
Pour the mixture through, pressing gently to extract the syrup. Don’t push too hard or the syrup may turn cloudy.
Cool completely: Let the syrup come to room temperature, then chill in the fridge for at least 1 hour. Cold syrup blends better with bubbles.
Assemble the fizz: Fill a glass with ice.
Add 2–3 tablespoons of the chilled syrup. Top with 6–8 ounces sparkling water or club soda and stir gently.
Make it boozy (optional): For a cocktail, add 1–1.5 ounces gin or vodka before topping with bubbles. Stir softly to combine.
Garnish and serve: Add strawberry slices, a lemon wheel, or a sprig of mint.
Serve immediately while it’s nice and fizzy.
Batch option: For a pitcher, combine 1 cup syrup with 4 cups chilled sparkling water and plenty of ice. Add alcohol to the glass, not the pitcher, to keep it flexible.