1Slice the red onions very thinly, then place them in a colander and sprinkle with a pinch of salt. Let them rest for 15 minutes to draw out excess moisture, then squeeze them gently to remove any remaining liquid.
2In a large bowl, whisk the eggs. Add the 00 flour, grated Parmigiano-Reggiano, finely chopped fresh parsley, baking powder, salt, and freshly ground black pepper. Mix well until you have a smooth, thick batter.