Tempura Batter

1/2 cup (3 ounces) cornstarch
1/2 cup (2 1/4 ounces) all-purpose flour
Kosher salt
1 large egg
1/4 cup (60ml) 80-proof vodka
1/2 cup (120ml) ice-cold club soda
4 cups thinly sliced vegetables or 1 pound (450g) shrimp (see note)
Lemon wedges, for serving