To make the crumbs: Sift the 4 cups flour and then mix in 1-1/3 cups sugar, cinnamon and salt in a large bowl. Mix in the 1 pound melted butter, 3 tsp. vanilla, 1 tsp. butter flavor. The crumbs mixture should have a consistency of wet sand. (You can add more flour/sugar if needed). When done, store in refrigerator.
To make the cake: Grease a large lasagna style pan (12 x 17) and shake flour into it to coat it. Mix the cake ingredients together thoroughly in a large bowl: the yellow cake mix (DON'T follow any instructions on the cake mix box!!), 3 eggs, 1-1/3 cups water, 1-1/2 tsp. vanilla, and 1-1/2 tsp. butter. Pour into the lasagna pan and bake for 15 minutes at 350 degrees. Remove from oven and "crumble" the crumbs mixture evenly over the partially-baked cake. You can grab a large chunk and use a cheese grater to do this. Return to the oven and bake for 15 minutes longer, or until a toothpick comes out clean when inserted into the cake. Cool completely and sift powdered sugar over the crumbs. Cut cake into pieces before taking it out of the pan.