Combine flour, butter, shortening, salt in a food processor. Pour in water until dough comes together. Shape into a disk. Wrap and place it in the refrigerator overnight.
Plum Filling
Roll out dough flat and round. Arrange sliced plums on top. Sprinkle with cinnamon and chopped nuts. Pour Just Date Syrup on top. Cut up butter into small pieces and place on top of the galette. Fold up the edges of it all around the sides.Bake in a 350 degree oven for 35-45 minutes or until browned. Cool on wire rack.
Frozen Whipped Cream
Combine all ingredients in a stand mixer. Whip until there are stiff peaks. Place in a bowl and cover. Freeze over night. When ready to use, use an ice cream scoop and scoop out the frozen cream and place on top of galette.