Preheat oven to 325℉ (160℃). Grease a 9x13-inch pan.
To make crust: In a large mixing bowl, beat together the margarine or butter, flour, and confectioners' sugar until fluffy. Scrape mixture into the pan and smooth. Bake 15 minutes.
To make filling: In a medium bowl, beat the eggs and sugar. Grate the rind of the lemon and add the rind, along with 6 tablespoons of lemon juice, to the egg mixture. Sprinkle 1 tablespoon of flour and the baking powder over the mixture. Fold in the nuts and mix until well blended.
Remove crust from oven. Pour the lemon mixture into crust.
Bake for another 35 minutes, until filling is set. Let cool before cutting.