Meanwhile, for the sauce, heat a large saute pan over high heat and add a 3-count of olive oil(about 3 tablespoons). Add mushrooms and cook for 3 minutes, until brown. Add garlic and shallots and toss to combine. Season with salt and pepper. Cook for 2 minutes more, until garlic and onion become fragrant. Remove pan from heat and carefully add cognac, scraping to deglaze the pan. Return to heat and add whipping cream. Reduce heat and simmer, until reduced by half. Turn off heat and stir in mustard and sour cream. Season with salt and pepper. Keep warm until ready to serve.