Preparation Cut asparagus tips into 2-inch-long pieces; set aside. Peel asparagus stalks. Cut stalks into 1-inch pieces. Cook stalks in large saucepan of boiling slightly salted water until very tender, about 10 minutes. Using slotted spoon, transfer stalks to blender. Add 3/4 cup cooking liquid to blender. Blend until very smooth, adding more cooking liquid to thin sauce. Blend 2 tablespoons butter into sauce. Season with salt and pepper. (Sauce can be made 8 hours ahead. Cover and refrigerate.) Transfer sauce to medium saucepan. Bring sauce to simmer. Remove from heat. Cover to keep warm. Cook asparagus tips in boiling salted water until crisp-tender, about 4 minutes. Drain. Sprinkle fish with salt and pepper. Melt 2 tablespoons butter in each of 2 heavy large skillets over medium-high heat. Add 3 fish fillets to each skillet and cook until golden and opaque in center, about 4 minutes per side. Spoon warm sauce onto plates. Top with fish. Garnish with asparagus tips. Sprinkle with fennel seeds and serve.
Preparation Cut asparagus tips into 2-inch-long pieces; set aside. Peel asparagus stalks. Cut stalks into 1-inch pieces. Cook stalks in large saucepan of boiling slightly salted water until very tender, about 10 minutes. Using slotted spoon, transfer stalks to blender. Add 3/4 cup cooking liquid to blender. Blend until very smooth, adding more cooking liquid to thin sauce. Blend 2 tablespoons butter into sauce. Season with salt and pepper. (Sauce can be made 8 hours ahead. Cover and refrigerate.) Transfer sauce to medium saucepan. Bring sauce to simmer. Remove from heat. Cover to keep warm. Cook asparagus tips in boiling salted water until crisp-tender, about 4 minutes. Drain. Sprinkle fish with salt and pepper. Melt 2 tablespoons butter in each of 2 heavy large skillets over medium-high heat. Add 3 fish fillets to each skillet and cook until golden and opaque in center, about 4 minutes per side. Spoon warm sauce onto plates. Top with fish. Garnish with asparagus tips. Sprinkle with fennel seeds and serve.