In a stainless-steel bowl mix Dijon mustard, cranberry sauce, and mayonnaise; salt and pepper to taste; cover and refrigerate.
On medium heat add olive oil to the pan and the julienne of chopped onions; turn the heat to very low and simmer down, till onions are soft and caramelized; stir 5-6 times; the process should take approximately 70 to 75 minutes; let cool and transfer to a covered container.
Shred or slice gouda cheese, cover, and refrigerate.
Pre-slice cooked natural turkey breast or smoked/roasted turkey breast; cover and refrigerate.
Assemble the sandwich – add a generous layer of softened butter on the outside of the bread slice; transfer the buttered side down on a parchment-lined tray; on the unbuttered side add 20 grams of cheese and 2 oz of turkey meat.
Add 7 tbsp of cranberry mixture then 7 tbsp of caramelized onion.
Add 2 more oz of meat then 20 grams of cheese then top with bread; add another generous layer of butter to the top and transfer to the non-stick frying pan.
Fry on low to medium heat for 3-5 mins then transfer to other side and crisp till golden.
Transfer to the cutting board cut in half and serve with a side salad or chips.