Fill a pan with water. Add a pinch of salt, cover and bring to the boil. Scrub the potatoes. Chop them into equal-sized chunks. When the water is boiling, add the potatoes. Simmer for 10-15 mins till they’re just soft.
Meanwhile, rinse the chestnut and portobello mushrooms. Slice the larger mushrooms. Peel the onion and finely slice it. Roughly chop the chervil. Peel and grate or crush the garlic. Finely chop the chilli, flicking out the seeds for less heat. Heat your oven to its lowest setting.
Warm 1 tbsp olive oil in a deep frying pan or wok. Add the mushrooms. Season with salt and pepper. Fry over a medium heat for 10 mins till they’re golden. Stir them every so often while they cook.
While the mushrooms fry and the potatoes simmer, whisk 1 tbsp balsamic vinegar with ½ tbsp olive oil. Season. Toss through the lamb’s lettuce. Set aside.
Tip the mushrooms out of the pan into a bowl and put them in the oven to keep warm. Add 1 tbsp oil to the pan. Add the sliced onion. Fry for 2-3 mins over a medium heat. Stir in the garlic. Drain the potatoes. Add to the pan. Crush slightly with a masher.
Fry the smashed potatoes for 10-15 mins till they have plenty of golden edges, stirring them while they fry. When they’re golden, stir in most of the chervil and a good pinch of the chopped chilli (keep the rest for later).
Taste the potatoes and adjust the seasoning. Divide the hash between 2 warm plates. Top with the mushrooms. Put the plates in the oven. Wipe the pan with kitchen paper and add another ½ tbsp oil to it. Turn the heat to medium-low.
Crack the eggs into the frying pan. Cover and fry for 2-3 mins till the yolks are set to your liking. Top the plates of mushroom hash with a fried egg each. Sprinkle over the remaining chervil and a bit more chopped chilli to serve.