Haddock Fillets on Mashed Potatoes with Mustard Sauce and Quail Eggs

Name: Haddock Fillets on Mashed Potatoes with Mustard Sauce and Quail Eggs
Ingredients: 600 grams starchy Potatoes; 4 tablespoons Butter; 2 tablespoons Pastry flour; 250 milliliters Vegetable broth; 240 milliliters Milk; 4 tablespoons medium hot Mustard; 1 pinch Sugar; 1 tablespoon Wine vinegar; 8 Quail eggs; Salt; freshly ground Pepper; 2 Onions; 2 tablespoons Vegetable oil; 150 milliliters dry White wine; 1 Bay leaf; 4 Haddock fillets (each 160 grams); 1 tablespoon Trout roe; Dill (for garnish)