Pork Roast with Cardamom Mushroom Sauce

Name: Pork Roast with Cardamom Mushroom Sauce
Ingredients: 3/4 cup coarse kosher salt; 3/4 cup sugar; 1 gallon cold water; 1 tablespoon black pepper; 1 1/2 cups onion , chopped (about 2 medium sized onions), divided into 3 x 1/2 cups; 6 tablespoons extra virgin olive oil; 2 1/4 teaspoons ground cardamom , divided, 2 and 1/4 teaspoons; 1 large clove garlic; 1 4 - pound center-cut boneless pork loin roast; Salt and pepper; 1 1/2 pounds mushrooms , sliced; 2 cups chicken stock , divided, 1 cup and 1 cup; 1/2 cup heavy cream; 1 tablespoons all-purpose flour; 1 tablespoons butter , room temperature