Combine the mashed raspberries, honey, and water in a saucepan and heat gently over low to medium heat, stirring occasionally, just until the raspberries release aroma and the honey fully dissolves; do not boil hard or reduce. Remove from heat, add the lemon zest, cover, and let steep for about 10 minutes, then strain through a fine-mesh sieve and allow the syrup to cool completely.
Add the lemon pulp and the lightly mashed raspberries to a large pitcher and gently muddle just enough to release juice and aroma without crushing seeds into bitterness or turning the mixture into purée.
Pour the cooled honey–raspberry syrup into the pitcher, add the fresh lemon juice and the fine sea salt, and stir to combine; add the ice-cold water and stir gently until fully integrated. Taste and adjust only with additional cold water if needed — sweetness and acidity should already be locked.
Refrigerate for 1–2 hours until fully cold and the flavors are fully aligned.
Fill glasses with ice, pour over the raspberry lemonade, and garnish with lemon slices and fresh raspberries.
