In a food procesor, add the flour, sugar, cinnamon and salt. Add the cold butter and shortening, pulsing until they are cut into the flour, looking like large pebbles. Add the cold water then pulse until the dough comes together.
Flatten the dough into an evenly round disk and wrap in plastic wrap. Refrigerate at least 1 hour or until cold.
While the dough is chilling, toss the apples slices with the lemon juice.
Once the dough is cold, roll it out into a 10-inch circle. Place dough on a greased baking sheet or round pizza pan. Work fast as the dough will warm quickly.
Spread the apple butter on top of the dough, leaving a 1 inch border around the edge. Arrange the apple slices in a single layer on top of the apple butter. Top with walnuts.
Fold the edges of the pie crust over, touching the filling. Sprinkle the cinnamon sugar over the galette. Preheat the oven to 425°F while you refrigerate the raw galette for 15 minutes.
Bake for 25 minutes or until the crust is golden brown. Immediately brush with a few teaspoons of apple butter after removing from the oven. Cool for 15 minutes before serving.