In a medium saucepan, combine strawberries, sugar, and ½ cup water. Bring to a gentle simmer over medium heat, stirring occasionally. Once the sugar dissolves completely (about 5 minutes), reduce heat to low and let simmer for another 5 minutes until strawberries soften and release their vibrant color.
Remove the saucepan from heat and add the fresh basil leaves. Cover and allow the mixture to steep for 20 minutes. The residual heat perfectly extracts the essential oils from the basil without cooking away the bright, herbaceous notes.
Pour the strawberry-basil mixture through a fine-mesh strainer into a large pitcher, pressing gently with the back of a spoon to extract all the liquid without forcing pulp through.
Add the freshly squeezed lemon juice to the strawberry-basil syrup, then pour in the remaining cold water. Stir thoroughly to combine all flavor elements.
For optimal flavor development, refrigerate for at least 1 hour before serving.
Fill glasses with ice, pour the chilled Strawberry Basil Lemonade, and garnish with fresh strawberry slices and small basil leaves.