Spread sugar on a small plate. Rub rims of 2 cocktail glasses with lemon wedge. Dip rims in sugar to coat.
Fill a cocktail shaker half full with ice. Add whiskey, lemon juice, orange liqueur, and raspberry liqueur. Cover and shake until outside of shaker is frosted, about 60 seconds. Strain into prepared glasses. Top each cocktail with 1 1/2 ounces sparkling water and garnish with a raspberry.
A classic sidecar calls for Cognac, orange liqueur, and lemon juice, but this PB&J-inspired rendition subs in peanut butter whiskey and adds raspberry liqueur. Top it off with sparkling water for an effervescent cocktail with a hint of nostalgia.