You can either do the base in a bowl, or a food processor fitted with a steel blade.
Combine flour, sugar, baking soda, and lemon peel. Cut in the butter and egg with a fork, or, if using the food processor, with five-second pulses, until the mixture looks like coarse crumbs. Set aside two cups of this mixture. Press the rest evenly into an ungreased jelly roll pan (15 1/2 x 10 1/2 inches), and bake for 8 minutes.
In a 2-quart saucepan over medium-high heat, combine all the filling ingredients. Keeping an eye on it and stirring frequently, cook for about 8 - 15 minutes, or until the sauce has thickened to a jam/spread-like consistency. Spread the filling evenly over the base, and sprinkle the reserved flour mixture over all. Bake for another 15 - 20 minutes, or until golden brown.