Start by taking a small pot and tossing in the blackberries and blueberries. Add the sugar, water, and lime juice. Using a wooden spoon, mix everything together. This mixture is the base of your syrup and will bring out the beautiful flavors of the berries.

Set your pot on medium heat and bring the berry mixture to a gentle simmer. During this time, keep stirring and occasionally pressing down on the berries. This helps release their delightful juices and enhances the syrup's flavor. Allow it to simmer for about five minutes.

Once the mixture has simmered and thickened slightly, you’ll want to strain it. Take your fine strainer or cheesecloth and place it over a bowl or another pot. Carefully pour the berry mixture through the strainer, using a spoon to press the berries down and extract as much syrup as possible. Discard the solid parts once you’ve gotten all the juice!

Now for the moment we’ve all been waiting for! Fill each glass with ice (this adds an extra chill factor). Add about 2-4 tablespoons of your freshly made berry syrup over the ice. Top it off with the chilled lemon-lime soda and stir gently to mix.

Lastly, drop in a few fresh berries for added flair and, if you want an extra touch, top with a mint leaf. Serve immediately and enjoy the cheers and smiles that come with this festive mocktail!