While pork is cooking in the oven add onion and oil to the stovetop skillet the pork was searing in. Cook until onion is tender.
Add chicken broth and deglaze the pan by scraping off the burnt bits on the skillet to incorporate them into the liquid.
Cook on high, letting liquid reduce to ~1/3 cup.
Remove pork from the oven and let rest when finished cooking. Pour any pooling juices into the sauce.
Add maple syrup, balsamic vinegar, and mustard and stir to combine. Continue to cook until the mixture thickens into a sauce consistency. Turn down the heat as it begins to thicken.
When sauce is nicely thickened, add a few grinds of fresh pepper and butter. Stir the butter into the sauce until melted. Taste for salt and adjust as needed.