Bring a large pot of lightly salted water to a boil. Place pasta in the pot, cook for 8 to 10 minutes until al dente and drain. Cool, transfer to a large bowl and toss with 3 tablespoons olive oil.
Heat remaining olive oil in a large frypan over medium heat. Place mushrooms and onions in the frypan. Cook and stir until lightly brown. Gradually pour in the cream, stirring continuously. Place the mint sprigs in the frypan. Cook and stir 5 minutes.
Mix sugar into the cream sauce. Season with salt and pepper. Remove the mint sprigs with a slotted spoon. Stir in the cooked pasta until well coated.