Preheat oven to 350°F. Butter or spray a large loaf pan. In a large bowl, cream together butter or oil and sugar. Stir in applesauce, eggs, orange juice and vanilla.

In a second large bowl, whisk together flour, baking powder, and salt. Stir flour mixture into butter-egg mixture until just combined. Gently stir in blackberries.

Spoon batter into pan and bake until a toothpick inserted in the center of a muffin comes out clean, about 35-40 minutes.