Whisk the sour cream, mayonnaise, and lime juice together in a small bowl to create the creamy white sauce, then refrigerate until needed.

Combine the all-purpose flour, cornstarch, baking powder, garlic powder, paprika, and kosher salt in a large mixing bowl.

Pour the cold lager beer into the dry ingredients while whisking continuously until a smooth batter forms, then let it rest for 10 minutes.

Heat the vegetable oil to 350 degrees F in a heavy-bottomed pot or Dutch oven.

Pat the fish strips dry with paper towels to ensure the batter adheres properly.

Dip each piece of fish into the batter, letting the excess drip off, and carefully lower it into the hot oil.

Fry the fish in small batches for 4 to 5 minutes until deeply golden brown and crispy, then transfer to a wire rack or paper towel-lined plate to drain.

Warm the flour tortillas in a dry skillet over medium heat.

Assemble the tacos by layering the fried fish, shredded green cabbage, shredded red cabbage, shredded cheese, and chopped fresh parsley inside the tortillas.

Drizzle the tacos with the creamy white sauce and serve immediately with fresh lime wedges.