Irish Guinness Brown Bread

Name: Irish Guinness Brown Bread
Ingredients: 1 cup quick-cooking oats (not instant), such as McCann's, plus extra for sprinkling; 2 1/4 cups whole wheat flour, such as Heckers; 1/4 cup all-purpose flour; 1/2 cup dark brown sugar, lightly packed; 2 1/4 teaspoons baking soda; 1 teaspoon baking powder; 2 teaspoons kosher salt; 1 (11- to 12-ounce) bottle Guinness extra stout beer, at room temperature; 1 cup buttermilk, shaken; 5 tablespoons unsalted butter, melted, plus extra for brushing the pan; 1 teaspoon pure vanilla extract; Salted butter, such as Irish Kerrygold