Bring a large pot of water to a boil and salt generously. Cook the pasta according to the packet directions.

While the pasta is cooking, heat a large frying pan over medium heat and add half the butter and bacon and fry until the bacon is crisp. Add the remaining butter and red onion and fry for a further minute or two until the onions have just softened. Add the vinegar and mustard and stir to combine. Add the pasta to the pan with a little pasta water and toss to combine. Add the parsley and plenty of freshly ground black pepper and toss together.

Set your immersion circulator to 75°C. Once at temperature, lower the eggs (still in their shells) into the water bath and cook for 12 minutes. The whites will be just set while the yolk stays gloriously runny. Carefully crack each egg directly over a serving of pasta and finish with a light sprinkling of parmesan cheese.