2) Place the eggs into an electric kettle and cover with cold water by at least 2cm. Turn the kettle on. Once the water comes to a boil, the kettle will turn itself off. Leave the eggs in the water for 15 mins. Remove and peel off the shell. Slice each egg into 8 pieces and set aside.
3) While the eggs are cooking, fry the streaky bacon and remove to a paper towel to drain, reserving 3 tbsp of the rendered fat. Crumble the bacon and set aside.
4) Transfer the fat to a small saucepan set over low heat and whisk in the red wine vinegar, sugar and Dijon mustard. Season with a small pinch each of salt and black pepper.
5) Add the mushrooms and the sliced onion to the spinach and toss. Add the dressing and streaky bacon and toss to combine. Divide the spinach between 4 plates or bowls and evenly divide the egg among them. Season with pepper, as desired. Serve immediately.