Toast the walnuts in a large dry pan over medium heat. Keep an eye on them and shake the pan often to prevent the walnuts from burning. Once the edges start to brown, place the walnuts onto a heat-safe dish.
Add the olive oil to the still-heated pan. Add the onions and garlic and sauté for about 4 minutes, until the onions soften and turn translucent. Add the mushrooms, parsley, rosemary, salt, and pepper into the pan. Sauté for another 5-8 minutes, until the mushrooms are cooked and decrease in size.
Allow the mushrooms and walnuts to cool. Once they are cooled, add them into a food processor. Pulse and stop to scrape the sides as needed until it reaches the texture of pâté. Allow the pâté to cool completely in the fridge before serving. Makes about 1 2/3 cups of pâté.
Notes:
Serve with toast, french bread, or sourdough bread.
