In a medium bowl, whisk together ½ cup whole milk, ¼ cup sour cream, and 1 tablespoon lemon juice until creamy. Dredge shrimp in this mixture and soak for about 5 minutes.

In another bowl, mix 1 cup all-purpose flour, ½ cup cornstarch, 1 teaspoon salt, ½ teaspoon black pepper, and 1 teaspoon paprika until well-blended. Coat soaked shrimp in the flour mixture.

Heat oil in a large skillet to 325°F. Ensure it reaches a depth of 1-1½ inches for frying.

Carefully place the shrimp in hot oil, frying until golden brown and crispy, about 2-3 minutes per side.

Combine ½ cup mayonnaise, ¼ cup Thai sweet chili sauce, 1 tablespoon minced garlic, and 1 tablespoon Sriracha in a large bowl. Toss crispy shrimp in this sauce until evenly coated.

Transfer the shrimp to a serving platter, garnish with green onions if desired, and serve immediately.