Mix crumbs and chopped nuts. Reserving 1/2 cup, mix 1 cup crumb mixture with melted butter. Press into the bottom of an 8-x8-inch baking dish. Bake in a preheated 400-degree oven for 10 minutes. Remove from oven and allow to cool thoroughly. Grate lemon rinds and then juice lemons. In a medium bowl, mix sweetened condensed milk, lemon juice, and lemon rind thoroughly. Pour on top of baked crumb mixture and spread carefully. In a clean mixer bowl with clean beaters, beat whipped cream on high speed until stiff peaks form. Spread over mix and lemon layer. Scatter reserved 1/2 cup crumb mixture over whipped cream layer and refrigerate. Do not substitute artificial whipped topping for whipped cream.