Stir together brown sugar, cinnamon and flour. Add butter; blend with a fork until the mixture resembles coarse crumbs. Stir in nuts. Set aside
Preheat oven to 350°F. Butter a 9×5–inch loaf pan or line the pan with waxed or parchment paper.
Whisk together flour, baking soda. and salt in a bowl and set aside.
Cream butter; gradually add sugar and beat until light and fluffy. Beat in eggs and vanilla. Add dry alternating with buttermilk and mix just until smooth. Fold in apples and nuts.
Pour batter into a large (9×5-inch) loaf pan. Top with streusel mixture. Bake 50 minutes or until wooden toothpick inserted in center of bread comes out clean.