Bring 2 cups of water to a boil in a medium saucepan over high heat. Once boiling, add the sugar and stir constantly until completely dissolved, about 1-2 minutes. Add the rhubarb pieces and strawberries, then reduce heat to medium and simmer for 3-5 minutes until the fruit begins to break down and release its juice. Remove from heat and let the mixture cool to room temperature—this takes about 30 minutes. Once cooled, strain through a fine-mesh sieve into a bowl, pressing gently on the solids to extract all the flavorful liquid. You should have roughly 2-2.5 cups of vibrant fruit syrup. I like to discard the cooked fruit rather than keeping it since the flavor is already captured in the syrup, giving you a clean, clear base for the fizz.

In a large pitcher or punch bowl, combine the gin, the store-bought simple syrup, and freshly squeezed lemon juice. Add a generous amount of ice—roughly 3-4 cups—to chill the mixture and begin diluting it slightly. This combination creates the aromatic backbone of your fizz, with the gin's botanicals complementing the tartness of the lemon. I find that adding ice early helps the drink reach the right temperature and dilution level before the final components are added.

Pour the cooled rhubarb-strawberry syrup from Step 1 into the pitcher with the gin mixture from Step 2, stirring gently to distribute the fruit flavors throughout. Add the chilled Moscato and lemon slices, then stir gently to combine without over-stirring, which can deflate the drink. Let the pitcher sit for 5 minutes to allow the flavors to marry and meld together, creating a more cohesive taste. For serving, I like to garnish each glass with a fresh rhubarb stalk and a small strawberry speared on a cocktail pick for both visual appeal and a hint of natural sweetness, then add a lemon slice and a mint sprig if desired for aroma.