In a small bowl, combine 2 1/2 teaspoons of the fresh rosemary, pepper and salt.
Slice the tenderloin into 1-inch thick slices. and distribute the rosemary mixture of the pork tenderloin, making sure to coat both sides of the medallions.
In a large skillet on medium high heat, pour olive oil.
Oil will be ready when a small drop of water placed into it sizzles.
Place the medallions into the skillet and cook for 3 minutes without touching.
With a small hard spatula or offset spatula, gently flip the medallions to cook on the other side for an additional 3 minutes and cover.
Transfer the medallions to a plate and cover with tin foil while making the sauce.
Reduce the temperature of the skillet to medium.
Mushroom Wine Sauce
In the skillet, melt the butter.
Sauté the mushrooms until soft, about three minutes.
Add flour and mix until well combined, any moisture will be absorbed.
Whisk in the wine and chicken base and bring to a boil.
Reduce heat and add cream, remaining teaspoon of rosemary, and sage.
If you'd rather not use the wine in the sauce, here are some things you can substitute it with - chicken broth/stock, vegetable stock, white grape juice, ginger ale, canned mushroom liquid, or diluted white wine or cider vinegar.