In a large saucepan, fry the sliced leeks in a drizzle of olive oil. Add the sliced fennel and the broth and cook on medium heat for 20 minutes, until the fennel is tender. Add the chickpeas and the grated Grana Padano Riserva, season with salt and pepper and, using an immersion blender, purée everything until the mixture is smooth and creamy.
Cut the sea bass fillets into slices, grease with a drizzle of olive oil and cook in a non-stick pan on both sides; season with salt and pepper.
Serve the sea bass hot on the warm leek cream, garnished with fennel fronds and chives.