Add sugar, dried lavender, and 1 cup of water to a small saucepan. Heat on low and stir often until the sugar is dissolved.
Let the syrup simmer for 2 minutes, then remove from heat and let steep for 15 minutes.
Strain the syrup through a fine mesh strainer to remove the lavender flowers.
Juice the lemons using the juicer. Try to remove any seeds.
Place raspberries in a bowl or directly in the pitcher. Gently mash with a muddler or fork.
Add the strained lavender syrup, fresh lemon juice, and 4 more cups of cold water to the pitcher with raspberries. Stir well.
Fill serving glasses with ice. Pour the lemonade mixture over the ice.
Garnish each glass with extra raspberries, lemon slices, and mint leaves if using. Serve cold.