Preheat oven to 375 F.
In a food processor, purée ½ an onion, grainy mustard, marmalade, butter, salt and pepper.
Place pork roast (doesn’t matter if tied or untied) in a roasting pan and slather with mustard glaze.
Arrange remaining sliced onions, pears, orange and fresh herbs around pork loin.
Roast uncovered for 15 minutes, then reduce oven temperature to 350 F, roasting for about 75 minutes, until an internal temperature of 175 °F is reached.
Remove roast from pan and let rest on a cutting board or platter for 15 minutes before slicing.
For pan juices, remove orange segments, thyme and sage sprigs, and discard. Place pan over medium heat and add white wine, stirring to pull up any caramelized bits from the bottom of pan.
Add chicken stock and sage and simmer until reduced by half. Reduce heat to low and stir in cold butter just until melted.
Season to taste and serve beside slices of roast pork.