In a 10-inch skillet heat the oil over medium high heat and add the garlic, ginger, serrano, garam masala, cumin, coriander, and turmeric. Cook stirring constantly until the garlic, ginger, and spices are aromatic but do not brown.
Add the onion, salt and pepper and lower the heat to medium. Cook stirring often until the onion is softened and caramelized (well brown) but do not burn. If the mixture starts to stick to the pan add a tablespoon of water and stir more often.
Add the potatoes, peas, and water. Cook until all the water has been absorbed by the potatoes. Mash the peas and potatoes while stirring. It is finished cooking once the water is gone and the potatoes are heated through. Cool this mixture.
Heat the oven to 400 degrees F. Roll the puff pastry out so that you can get 2- 6 inch circles out of each sheet. Cut each circle in half. Poke the dough with fork, about 6 times per piece.
Evenly distribute the filling into each the of the dough semicircles. Brush the sides with egg, fold over and press to seal. Place the finished samosa on a baking sheet lined with parchment. Continue until you finish all the filling or the pastry. Brush all the samosas with egg and place in the oven. Bake for 15 to 20 minutes or until the dough is golden brown.
In the meantime make the chutney. Combine all the ingredients EXCEPT the yogurt in the blender and puree. Fold in the yogurt and taste. Season with salt and pepper if needed.
Serve the hot samosas with the chutney.
Notes
Keep the dough as cold as possible. If you are not cooking the samosas directly after making them store them in the refrigerator until you are ready to put them into the oven.