In a large saute pan cook bacon until crispy. Remove bacon to a small bowl. Reserve bacon fat.
Melt butter in pan with bacon fat. Over medium heat add sugar, Worcestershire, and soy sauce. Cook, stirring frequently, until very bubbly and the sugar caramelizes. You can reduce this sauce for a minute or two to thicken if you prefer.
Add bacon and sliced onion. Remove pan from heat. Add spinach and stir gently to coat. Serve immediately.