Asparagus with Perch
Peel asparagus and snap off woody ends. Peel onion, halve lengthwise and cut into thin strips. Heat 1 tablespoon olive oil in a large frying pan. Add onion and cook until translucent. Add broth and mustard seeds and bring to a boil. Add asparagus, cover and simmer over low heat, about 8 minutes. Cut fish fillets into 3 cm wide (approximately 1-inch wide) pieces and season with salt and pepper. Heat remaining oil in a nonstick skillet. Add fish fillets, skin-side down, and saute 3-4 minutes. Flip fish and remove the pan from the heat. Cover and let steam about 2 minutes.
To serve, divide asparagus among preheated plates, sprinkle with dill and horseradish and season with salt. Ladle pan juices over asparagus and top with perch fillets.