Blend the base by combining fresh lemon juice, granulated sugar, fresh raspberries, and 1 cup of cold water in a blender. Blend for about 30 seconds until smooth.

Strain the blended mixture through a fine mesh sieve into a large bowl or pitcher to remove seeds and pulp. Press with a spoon for 3-5 minutes.

Combine strained lemonade with the remaining 3 cups of cold water, stir well, and adjust sweetness if needed.

Whip the heavy whipping cream and vanilla extract in a separate bowl until soft peaks form, about 2-3 minutes.

Fold in 1 cup of the lemonade mixture into the whipped cream gently for a marbled effect.

Serve by filling glasses with ice cubes, pouring the pink lemonade, and topping generously with the whipped cream. Garnish with raspberries and lemon slices.