In a bowl or zip-lock bag, combine the maple syrup, mustard, lemon juice and soy sauce. Pour over the pork (or place the pork in the bag), add the rosemary and let sit for half an hour, or refrigerate for a few hours, or overnight.
Preheat the oven to 400˚F.
Heat a drizzle of oil in a large ovenproof skillet over medium-high heat.
Remove the pork from the marinade, reserving the marinade, and brown the tenderloins on all sides, turning as necessary.
Slide the skillet into the oven for 15-20 minutes, or until the internal temperature reaches 160°F. Transfer to a cutting board.
Don’t wash out the skillet—add the butter to it and sauté the apples or plums for 3-5 minutes, until they soften and caramelize on the edges.
Add the marinade to the pan and bring to a simmer, scraping up any browned bits on the bottom of the pan.
Add the cream and cook until the mixture thickens slightly.
Serve the pork topped with the fruit and sauce.