For the vinaigrette, first squeeze the lemon. Mix 2 tbsp lemon juice with the salt, 1 tsp sugar and pepper, stir in 2 tbsp olive oil. Peel and wash the salsify and cut diagonally into 2 cm-long pieces. Blanche the salsify in salted boiling water for about 5 minutes. Meanwhile clean, wash and thoroughly drain the lamb's lettuce. Pat the salsify dry and sauté it while stirring with 2 tbsp olive oil in a pan for 4-5 minutes. Sprinkle with 2 tsp sugar, caramelise for 2-3 minutes. Place the salsify in a bowl, drizzle with vinaigrette, leave to marinate for 10 minutes. Fold the lamb's lettuce in and serve immediately.