Cook the pasta in a large saucepan of salted boiling water for 2 minutes less than packet directions. Ladle 250mL (1 cup) pasta water into a jug and reserve. Drain the pasta.
Meanwhile, combine the butter, parsley and 1 garlic clove in a small bowl. Reserve. Heat the oil in a large frying pan over medium heat. Add the onion, mushroom and remaining garlic. Cook, stirring, for 5 minutes or until tender.
Add the stock, cream and pasta. Bring to the boil. Reduce heat to medium-low. Simmer for 3 minutes or until sauce thickens and pasta is cooked, adding some reserved pasta water if too thick. Remove from heat. Toast bread and while warm, lightly brush 1 side of each slice with butter mixture. Stir dip and cheese through pasta. Season. Divide among serving bowls. Top with thyme, if using. Serve with garlic toast.
