Peel, core and slice about 1/4" thick. As you are slicing the apples, place the slices into a small bowl with lemon juice so as not to brown while they wait to be placed on top of the filling.
Take the blind baked pastry shell, fill with the applesauce filling.
Begin arranging the apple slices on top of the filling beginning on the outer edge and overlap as much or as little as you want keeping in mind that the apple slices will shrink. Continue moving around the tart until you reach the center. For the center, use four or five slices and place on end to create a flourish in the middle (upon baking they will fall flat, but the effect will be a blossom in the middle).
Melt the butter on the stove. Using a small brush, brush the apple topping with the melted butter and sprinkle with demerara sugar (or Mae's crumble).
Bake for 25-30 minutes or until the edge of the apples are quite dark and the rest of the tart is lightly brown. If the crust edges are becoming too dark before the apples become brown, use tin foil to cover and continue to bake until desired color of the apples is reached.
Let cool for about 10-15 minutes. Remove from the tart pan and serve with a hot cuppa, heavy whipped cream or dulce de leche gelato (Bonata is my favorite).