Bright and bubbly, this simple cocktail is as drinkable as it is endlessly riffable. For added sweetness, stir in an extra spoonful of jam, or try grilling your peaches for a hint of smoke that accentuates the tequila.
Place tequila, lime juice, and 1/4 cup jam in a cocktail shaker; muddle mixture. Fill shaker with ice. Cover and shake until thoroughly chilled. Place 1 tablespoon jam into bottom of each of 2 highball glasses. Fill glasses with ice, and strain tequila mixture into glasses. Top off cocktails with sparkling water. Garnish with grilled peach slices and lime twists.