Preheat oven to 375 degrees.
EGG WASH: Whisk egg and water together in a small bowl.
CRUST.
In a food processor, process the flour, butter, and salt until the dough forms a soft ball. Wrap in plastic wrap and refrigerate for 1 to 2 hours. This dough will be moist and softer than most pastry.
FILLING.
In a large saute pan, heat the oil and add onions, ginger, and garlic. Saute until onions are golden.
Add the potatoes, and saute for a few minutes more.
Add the spices and stir until mixed in well with the potato mixture.
Add the cilantro, lemon juice, and peas, stirring well. Remove from heat.
ASSEMBLY.
Leave about a third of the dough for the top crust. Roll out remaining dough to about 1/8 inch thick.
Line the springform pan with the dough, letting in hang over the top about 1/2 an inch.
Brush with the egg wash.
Pour in the filling and press down well.
Roll out the reserved dough, place over the pan, trim pastry and crimp edges sealing well. Brush with remaining egg wash.
Bake in oven for about 1 hour, until golden and heated through. Best made a day ahead and reheated at 350 for 40-45 minutes.
Serve with Raita.
