Roasted Duck with Jelly Glaze

Ingredients

Duck

4 duck breasts with the skin one

1 Tbsp kosher salt

1 tsp black pepper ( freshly ground)

1 tsp rosemary

Glaze

1/2 cup stock ( beef or chicken)

1/2 cup water

1/4 cup sherry vinegar

1/2  small onion or 1 shallot, finely chopped

2 Tbsp Jelly ( either a fruit oil a wine jelly will do)

1 tbsp unsalted butter