In a bowl using an electric mixer, or stand mixer with paddle attachment, cream the butter, sugar and salt together until creamy, about 2 minutes.
Mix in the applesauce, then add the flour and mix until incorporated. The dough will be rather clumpy. Use your hands to lightly knead the dough and form it into a ball inside the bowl.
Lightly spray a 9.5 inch tart pan with non-stick spray. Remove the ball of dough from the bowl and place on a lightly floured surface. Roll the dough out, large enough to fit the pan.
Transfer the dough to the pan and adjust with your hands to fit snuggly. Trim excess dough.
Place the tart pan with the unbaked crust in the freezer for 30 minutes.
Meanwhile, preheat the oven to 350 degrees F. After 30 minutes, remove the pan from the freezer and place on a baking sheet (for easy handling). Bake in the center rack of the oven for 23-26 minutes, until lightly golden. Let cool completely on a wire rack.