Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9 x 13 inch pan.
In a large bowl, mix dates, 1 teaspoon soda, and boiling water. Cool.
Add flour, 1 cup sugar, mayonnaise, and remaining 1 teaspoon soda. Use medium speed of mixer, and beat until mixture is well blended. Stir in nuts. Spread batter in prepared pan.
Bake for 45 minutes, or until a toothpick inserted in center comes out clean.
While the cake is baking, prepare the lemon sauce. Mix beaten egg and 1/4 cup water; place in a medium saucepan. Add 1 cup sugar, butter or margarine, and lemon peel and juice. Heat to boiling over medium heat, stirring constantly. Serve sauce over warm cake. Refrigerate any leftover sauce.