Mix milk, pumpkin, shortening, sugar, eggs, and salt together in a large mixing bowl using a hand mixer. Sprinkle yeast over mixture and stir gently until yeast is dissolved and well mixed. Mix in 2 cups flour at a time until mixture begins to get thick. Set mixer aside. Continue adding flour gradually, kneading by hand until dough is smooth and no longer wet and sticky. Place dough into a bowl, cover with a wet cloth, and set in a warm place until doubled in size, about 45 minutes. Roll out each dough portion on a lightly floured surface into a rectangle shape about 1/2-inch thick. Combine brown sugar and milk in a small bowl to form a paste; smooth sugar-milk paste evenly across both dough rectangles and sprinkle generously with cinnamon. Add apple, raisins, and walnuts. Roll up rectangles and slice into 1 1/2-inch sections. Place rolls into 7 greased pie pans, gently pressing down on rolls with your fingers to squish into the pans. Set rolls in a warm place until puffy, about 30 minutes. Preheat the oven to 350 degrees F (175 degrees C). Bake in the preheated oven until light brown, 10 to 15 minutes. Remove from the oven, tip rolls out of pans, and let cool on wire racks completely, 20 to 30 minutes. Melt butter in a saucepan over low heat and add brown sugar. Boil over low heat for 2 minutes, stirring constantly. Stir in milk and return to a boil. Remove from heat and let butter mixture cool to lukewarm temperature, about 10 minutes. Pour butter mixture into a mixing bowl. Beat using an electric mixer while adding powdered sugar gradually until it reaches a spreading consistency. If frosting gets too stiff, add warm water or more milk and beat. Frost cooled rolls with frosting.