Creamy Broccoli Pie

<li class="ingredient">Filling:<li class="ingredient">1/4 cup chopped sweet onion<li class="ingredient">1/4 cup thinly sliced celery<li class="ingredient">4 tablespoons butter<li class="ingredient">1/3 cup flour<li class="ingredient">1 teaspoon salt<li class="ingredient">1/2 teaspoon coarsely ground pepper<li class="ingredient">2 cups vegetable broth<li class="ingredient">2/3 cup half-and-half<li class="ingredient">3 to 4 cups broccoli pieces<li class="ingredient">1 tablespoon chopped pimiento<li class="ingredient">1 teaspoon Worcestershire sauce<li class="ingredient">Topping<li class="ingredient">2 cups biscuit baking mix<li class="ingredient">2 tablespoons shortening <li class="ingredient">1/3 cup milk<li class="ingredient">