1-To make beer batter: In a large bowl, combine flour, cornstarch, baking powder, and salt. Blend egg and beer, then quickly stir into the flour mixture (don’t worry about a few lumps).
2-To make white sauce: In a medium bowl, mix together yogurt and mayonnaise. Gradually stir in fresh lime juice until consistency is slightly runny. Season with jalapeno, capers, oregano, cumin, dill, and cayenne.
3-Heat oil in deep-fryer to 375 degrees F (190 degrees C).
4-Dust fish pieces lightly with flour. Dip into beer batter, and fry until crisp and golden brown. Drain on paper towels. Lightly fry tortillas; not too crisp. To serve, place fried fish in a tortilla, and top with shredded cabbage, and white sauce.