Place the duck confit on a baking sheet and heat for 10–12 minutes in the oven at 190 °C (375 °F). You can also brown the top of the confits for a few minutes under the broiler at the end of cooking.
Remove from the oven and wait 5 minutes before deboning them and coarsely shredding the meat. Place the four bun bottoms on a small platter and brush with a little Dijon mustard. Lay 1–2 slices of onion on each, then a portion of the duck confit meat. Then garnish with some of the Roquefort cheese.
Place under the grill for a few minutes to melt the cheese a little.
Immediately serve one burger per person and top with the chopped lettuce and sweet or hot pepper jelly. Serve with crudités and potato chips of your choice.