In a 2-quart sauce pan mix sugar, flour, salt and milk. Bring ingredients to a low boil and cook for two or three minutes, stirring constantly, until filling becomes thick. Remove pan from heat and add 1/2 cup of hot mixture to beaten egg yolks and whisk together. Place filling back on stove at a low heat and slowly pour egg yolks into filling while whisking together. Pour lemon juice and vanilla extract into filling and bring to a soft boil and cook for two to three minutes longer. When filling is thick, remove from heat and set aside to cool. The filling may be poured into the crust while still a little warm but not hot.
Place pie in refrigerator for several hours to set and chill completely. When chilled, top with Cool Whip and sprinkle the two Tbsp of crumbled cake crumbs over the top. Garnish with fresh lemon zest.Makes 4 Source: