Cut the onion in half, then peel it and cut it into 3-4mm (⅛") thick half-moon shapes.
Heat a small-medium (18-20cm or 7-8") saucepan that is not nonstick over a low heat, and when it is hot, add the oil and the onions. Slowly caramelise the onions for around 1 hour, stirring every 10-12 minutes.
If you are grinding your own meat, place the veal and the pork belly in your mincer with a coarse plate and pass them through once. If you are not grinding your own meat, but you are adding the pork belly, chop it as finely as you can with a sharp kitchen knife.
Add the salt and pepper to the meat and then form two evenly sized patties and sandwich them between two sheets of baking parchment and allow them to rest in the fridge for at least 1 hour. Make sure that you remove the patties from the fridge 10-15 minutes before cooking.
Once the onions are a deep brown, add in the sugar and stir until dissolved,
Turn up the heat to medium-high, then pour in the port and bubble down until sticky and dry, taste and add a pinch of salt.
Cut the slab of Gouda into two large squares, 1cm (just under ½") thick.
Take two baking trays that nestle into each other and place a layer of baking parchment in the first, followed by the Parma Ham, followed by another layer of baking parchment. Add the second baking tray, followed by another piece of baking parchment, then the Gouda cheese squares, then another piece of baking parchment.
Place the next baking tray in a preheated oven and cook for 12-15 minutes at 200°C or 400°F.
Heat a 28cm (11") frying pan over a high heat and oil both sides of the patty with a drizzle of oil. When the pan is hot, add the burgers and cook for 4-5 minutes on each side, then remove and set aside.
Toast the burger buns in the pan that you cooked the patties in for 30-60 seconds.
Now build your burgers, I start with rocket/arugula, followed by a burger, some onions, baked cheese, Parma ham, then iceberg lettuce and finally some more onions.