Chestnut Lamb Loin with Sweet Onion Marmalade

Name: Chestnut Lamb Loin with Sweet Onion Marmalade
Ingredients: 4 cups all-purpose flour; 1/4 cup sugar; 1 teaspoon baking soda; 1 tablespoon baking powder; 1/2 teaspoon salt; 1/2 cup (1 stick) butter, softened; 1 cup buttermilk; 1 egg; 1 tablespoon grapeseed oil; 1 large sweet onion (such as Vidalia), diced; 1 teaspoon curry powder; 1/4 cup golden raisins; 1 teaspoon apple cider vinegar; 3 pounds lamb loin; Salt and freshly ground black pepper; 1/2 cup chestnut puree (such as Marron's sold in a 15-ounce jar); 1 tablespoon stone ground mustard; 1/2 cup ground instant oatmeal