Reduce heat under pan to medium. Stir in remaining chopped rosemary, 1 TBSP vinegar (we'll use more later), maple syrup, stock concentrate, and ¼ cup water. Let simmer until thickened, about 1 minute. Stir in 1 TBSP butter, then season with salt and pepper. Return pork to pan, tossing to coat in sauce, then remove pan from heat.