1Heat 3 cups oil in a large deep pot over high heat until temperature reaches 365°F. Meanwhile, combine flour, salt and sugar in a large bowl.
Mix egg, milk and remaining oil in a small bowl. Slowly add liquid ingredients to dry ingredients, stirring with a fork or whisking until smooth.
Pat pineapple rings completely dry. Dip each ring into batter, letting excess drip back into bowl.
Lower rings gently into hot oil with a slotted spoon, 2 at a time. Fry until golden brown, about 2 minutes. Drain well on paper towels. Sprinkle with confectioners' sugar.