Preheat oven to 350
Salt and pepper the roast.
Mix the garlic and rosemary together. Add tbsp of the olive oil and mix well.
In a cast iron skillet heat the other 2 tbsp olive oil. Add the roast and seer all sides. Remove from heat. Generously put the garlic rosemary mix on the roast.
Place the skillet in the oven and cook for 1 hour or longer depending on how rare you like your roast. Mine took 1hr 20 minutes.
Once roast done, take out of skillet and let rest.
Using the juices add stock to the skillet on the stove top. Add mushrooms and 2 tbsp butter and let cook down.
To serve cut roast and place mushroom mixture on top. Garnish with Rosemary.