Cream butter and brown sugar. Add flour and chopped nuts and place into a well buttered tart pan or a 13x9-inch pan. Bake in a 350 degrees F oven for 15-30 minutes or until golden brown.
Meanwhile, melt the lemon Jell-O in 1 cup of hot water and let cool for 10-15 minutes or until no longer warm to the touch. Cream the 3/4 cup sugar with the softened cream cheese, whipping cream, and cooled lemon Jell-O. Pour the cream cheese mixture into the cooled crust and refrigerate for 8 hours or overnight.
Melt the boxes of lime Jell-O in 3 cups of hot water and let cool for 10-15 minutes or until cool to the touch. Pour lime Jell-O over filling and refrigerate until set. Cut into 2 inch squares, clean the knife for each cut.