• Lightly score the skins of the duck breasts and rub with salt. Place into a non stick pan on a medium to low heat skins sides down. Add the chopped onion to the same pan and cook for 18-20 minutes regularly stirring the onions in the rendered duck fat. Occasionally turn the duck over to cook lightly on the underside but cook skin side down for much longer. Remove the duck and set aside to rest.
• (Optional) add the mushrooms and pepper and fry for 3-4 minutes and remove from the heat.

Cheese Sauce

• Melt the butter in a pan on a medium heat and add the flour and stir to fully incorporate. Continue to stir the roux on the heat for 2-3 minutes. Add the milk and whisk until thickened to a light bechamel.
• Stir in the grated cheeses until melted and add the gochujang chilli paste, set aside.
• Bake the bread rolls in the oven for 5-6 minutes to heat up. Slice in half.
• Remove the onions, mushrooms and peppers from the pan. Turn up the heat on the hob and return the duck breasts skin side down to the pan. Fry for 2-3 minutes to crisp up the skin.
• Place the duck breasts on a chopping board and cut into bite sized pieces.
• To build your duck sandwiches, spoon a generous layer of onion over each bottom bread slice. Top with the duck pieces followed by the mushrooms and peppers. Pour over the cheese sauce and place the top slice on top and serve.