Remove the stems from the spinach and wash and pat dry thoroughly.Place into a large mixing bowl and set aside.Peel eggs and slice into 8 pieces.Fry the bacon until crispy and remove and drain on paper towels.Crumble and set aside.Reserve 3 tablespoons of the rendered bacon fat.Transfer fat to a small saucepan on low heat and add wine vinegar, sugar and Dijon mustard, whisk to combine thoroughly.Season with a pinch of salt and fresh black pepper.
Add the red onion to the spinach and toss.Add the dressing and bacon and toss with spinach to combine.Divide the spinach between 4 salad plates and garnish with the hard-boiled egg slices.Season with additional freshly ground black pepper.