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 cup boiling water; 1 gallon cold water; 1 tablespoon pepper; 1 1/2 cups chopped onion (about 2 medium sized onions), divided into 3 x 1/2 cups; Olive oil; 2 1/4 teaspoons ground cardamom, divided, 2 and 1/4 teaspoons; 1 large garlic clove; 1 4-pound center-cut boneless pork loin roast; Salt and pepper; 1 1/2 pounds mushrooms, sliced; 2 cups chicken broth, divided, 1 cup and 1 cup; 1/2 cup whipping cream; 1 Tbsp all purpose flour; 1 Tbps butter, room temperature