In a large saute pan, add the olive oil and heat over medium-high heat. Add the shallots and mushrooms and season with salt and pepper. Saute until the liquid has evaporated and the pan becomes dry, about 5 minutes.
Add the garlic, rosemary and butter and stir until butter is melted. Remove from the pan to a bowl and cool completely.
Tawny Port Jus
In the same large saute, add 1 tablespoon butter and melt over medium-high heat. Add the shallots and saute until they become translucent, about 3 minutes. Add the bottle of wine & rosemary and turn the heat to high. Boil until the wine has reduced by half. Add the beef stock and continue to boil until the mixture has reduced by half (about 2 cups total remaining).
Strain the liquid through a fine meshed sieve into a clean small saucepan. Return to medium heat and add the butter and stir until melted. Turn to low to keep warm.
Roulade
Preheat the oven to 375 degrees F.
Place the butterflied lamb between 2 pieces of heavy parchment paper or plastic wrap. Pound until it's about 3/4 inches thick. Sprinkle with salt and pepper and cover with the duxelles. Roll from the wide end into a roll. Tie with kitchen twine to secure.
Using the same large saute (or an ovenproof large frying pan) heat 1 tablespoon olive oil over medium-high heat. Add the roulade and brown on each side, about 2 minutes per side.
Place in the oven and roast for 15-20 minutes. Remove and allow to rest for 10 minutes.
Cut into slices and drizzle with the Port Jus and serve.