Place quail eggs in a large pan of cold water, bring to the boil, and cook for 3-4 minutes for soft-boiled. Drain and refresh under cold water, then peel. Place the flour, beaten egg and breadcrumbs in separate bowls.
Remove sausage skin and divide meat into 12 portions. Flatten each portion to about 1cm thick, then wrap meat around an egg and roll to enclose. Coat the egg in flour, then in beaten egg, then crumbs. Repeat with remaining quail eggs.
Half fill a deep-fryer or large pan with sunflower oil. Heat to 190°C (a cube of bread will turn golden after 30 seconds). In batches, deep-fry eggs for 3-4 minutes until golden. Drain on paper towel.
Meanwhile, heat 1 tablespoon oil in a frypan over medium heat. Add the bacon and cook, stirring, for 2-3 minutes until crispy. Drain on paper towel. Set aside.
Add mushrooms to the pan and cook over medium-high heat for 2-3 minutes, stirring, until softened. Set aside.
Whisk vinegar, mustard, tarragon, garlic, sunflower oil and remaining olive oil together in a small bowl. Season.
Divide the salad leaves among plates. Top with bacon, mushrooms and halved Scotch eggs, then drizzle with dressing.
