Preheat the oven to 425°F (220°C).
In a large saucepan, combine the sugar, water, and cream of tartar over high heat, stirring occasionally. Once it boils, reduce heat to medium and boil for 20 minutes. Remove from heat, stir in the lemon juice, and allow to cool.
In a separate bowl, crush the Ritz crackers. Some large pieces are desired.
Fit your prepared bottom crust in a standard 9-inch (23-cm)pan (not a deep pie pan), and evenly place the crushed crackers inside. Pour the syrup mixture over the crackers before evenly sprinkling the ground cinnamon over the pie. Dot this filling with the pats of butter. Place the top crust over the pie and trim any excess. Seal and crimp the edges with a fork. Cut small slits in the top crust.
Beat the egg and water together to create an egg wash. Brush this over the top and edges of the pie.
Bake for 10 minutes, before reducing the temperature to 350° (180°C) for another 20 to 25 minutes, until the crust takes on a golden color. Let the pie cool to room temperature and solidify on a wire rack for 2 hours before serving. Pie may be refrigerated after this point before serving.
