Step by step
Prepare a filling with an electric hand blender, combining breadcrumbs, gorgonzola, walnuts, a little bit of the scooped out onion heart, and some salt and pepper
Tips
If you want to transform a recipe like this to one perfect for vegans, replace the butter with to olive oil and the cheese with one suitable for vegans.
Trivia
If you want to cut your onions without making yourself cry, try this cunning idea: wet the blade of your knife with some water before starting work.