Poached beef with herb vinaigrette leeks

Name: Poached beef with herb vinaigrette & leeks
Ingredients: 6 onions; 6 leeks; 2 tablespoons olive oil; 200 ml white wine; 3 litres organic vegetable stock; 1.25 kg beef-eye fillet , roughly 8cm in diameter; HERB VINAIGRETTE; 1 shallot; 6 cornichons; 1 bunch of fresh coriander; 1 bunch of fresh chives; 1 teaspoon Dijon mustard; 2 teaspoons wine vinegar; 2 teaspoon savora sauce , (see tip); 4 tablespoons rapeseed oil; 1 teaspoon capers