Gather and prepare all your ingredients. Finely chop the onion, garlic, and fresh sage.
Season the pork tenderloins generously with salt, pepper, ground sage, and mustard seeds on both sides.
In a large skillet or Dutch oven, melt the butter, ghee, or tallow over medium heat. Sauté the onions for a few minutes, until soft and translucent.
Stir in the applesauce, garlic, and fresh sage. Cook for about a minute, until fragrant.
While the mixture cooks, slice the tenderloins into roughly 1-inch medallions. Arrange the slices in the pan over the applesauce mixture.
Pour in the bone broth (or water), cover with a lid, and cook over medium-low heat for about 10 minutes. Then, use a fork to flip each slice and press the meat gently into the sauce. Cover again and cook for another 5 minutes, then uncover and let simmer for about 10 minutes more, or until the pork is cooked through.
Remove the pork from the pan and set aside. Let the sauce reduce over medium-low heat, stirring often, until thickened.
Return the pork to the pan and spoon the sauce over the medallions. Garnish with fresh sage, if desired, and serve warm.