Sprinkle tenderloins with salt and pepper on both sides of the meat.
Add oil to ovenproof pan (I used cast iron) and heat over medium heat. Once oil is hot, add pork loin to the pan.
Sear until browned on both sides (about 5 minutes per side).
Slide meat thermometer into thickest part of the meat and then put pan into oven. Cook meat for 35-40 minutes or until thermometer reads 150 degrees Fahrenheit.
While meat is cooking add butter to small saucepan and melt over medium heat.
Add onion to pan and cook until onion has softened.
Stir in marmalade, Grand Marnier and mustard. Cook until marmalade has melted and then an additional 2 minutes. Then remove from heat.
Once meat is cooked, remove from oven and place pork loin on a cutting board and cover with foil for 10-20 minutes to let the meat rest.
Take the pan that the meat was cooked in and place it on the cooktop over medium heat. Add the chicken broth and cook until liquid is reduced by half.
Pour the juice into the marmalade sauce and then stir in the orange zest.
Slice the pork and spoon Grand Marnier onions over sliced meat.
Serve.
Recipe by My Man's Belly at https://mymansbelly.com/2017/01/27/roasted-pork-loin-with-grand-marnier-onions/