Place the flour, butter, powdered sugar and walnuts into a blender or food processor. Blend until mixture becomes coarse crumbs. Alternatively, place ingredients into a bowl and mix with a pastry cutter.
Press mixture into a greased 9x13 baking pan. Bake at 350 degrees for 10-13 minutes. Do not brown.
Remove from oven and let cool.
Place the pudding mix, buttermilk and pie filling into a large bowl. Beat with mixer until well incorporated. Fold in whipped topping. If you have a hard time getting the whipped topping to incorporate, use a hand mixer. It will turn out just fine.
Spread onto crust and refrigerate until ready to serve.
Garnish with more whipped topping, if desired.
Notes
You can leave out the nuts or use your favorite nuts instead of the walnuts. Also, you can double the crust ingredients if you like a thicker crust.
Recipe by Mandy's Recipe Box at https://mandysrecipeboxblog.com/lemon-fluff-dessert/