Preheat oven to 350°F and spray 9 x 5 x 3-inch loaf pan with nonstick cooking spray.
Whisk together sugar, milk, oil, extract, yogurt, egg and lemon zest in a large bowl. Stir together dry ingredients and 3/4 cup walnuts and add to bowl, stirring just until dry ingredients are incorporated (do not over mix). Carefully fold in blackberries and spread in prepared pan; sprinkle with remaining walnuts.
Bake for 1 hour and 20 minutes or until a toothpick inserted into the center comes out clean. Refrigerate after 2 days.