Combine flour and salt in large mixing bowl, then stir in oil. Add water, little by little, to form a workable dough. Form the dough into a ball and wrap in a damp kitchen towel to rest at room temperature for 30 minutes.

Cover the potato with 1" of water in a medium saucepan. Cook until tender, then drain in a colander and coarsely mash it with a fork. Set aside.

Return saucepan to medium heat and melt the butter. Add onion plus ½ tsp salt and cook about 6 minutes, until translucent and just starting to brown.

Add jalapeño and ginger, cook a minute more, then stir in the spices. After about 30 seconds (when spices smell aromatic) add mashed potato, remaining salt, frozen peas and cilantro; stir until well combined, then transfer to the fridge to cool.

Divide the dough into 6 equal portions, then roll each into a ball. Roll each ball into a thin circle, then use a knife to slice in half lengthwise to make two half-circles. Take one half in your hand, brush some water on the edges, and fold into an open cone shape, pressing edges to seal. Hold the cone and fill with about 2 tbsp potato filling. Pinch to seal Allow it to sit on a cutting board to form a flat bottom. Finish shaping remaining samosas. You’ll have 12.