Wash the spinach and drain well. Fry the bacon in 2 portions in a large pan until crispy, remove and drain on kitchen paper. Heat half the butter in a large pan. Fry 2 slices of toast in it until crispy, take them out. Heat the remaining butter in the pan, fry 2 more slices of toast until crispy, remove.
Spread 1 tablespoon of mustard on each slice of toast. Cover with gorgonzola, spinach and bacon slices