For the raspberry syrup, place a fine-mesh strainer over a bowl. Place the defrosted berries in the strainer and let sit for 30 minutes to drain. With the back of a wooden spoon, press the fruit gently against the strainer so the juice going into the bowl stays clear and pulp-free. There will be 3/4 cup raspberry juice. This juice keeps, tightly covered in the refrigerator, for up to 3 days. Use it with club soda, in iced tea, or a smoothie.
Carefully drop 1 teaspoon of Chambord liqueur and 1 teaspoon of raspberry juice into the bottom of a chilled champagne flute. Add the Sweet’N Low®. Fill the glass 3/4 full with prosecco. Drop the raspberries into the glass or thread them on a toothpick and place it across the top of the glass