Prepare the filling
Boil potatoes in salted water until just tender (5–7 minutes). Drain and cool.
Cook chorizo in a skillet, breaking it apart until browned.
Add onion; cook until softened.
Stir in potatoes, season, and let mixture cool completely.
Make the dough
In a bowl, combine flour and salt.
Add cold butter; work in until mixture looks like coarse crumbs.
Beat eggs with cold water; pour into flour mixture.
Mix until dough forms; knead briefly.
Wrap and chill for 30 minutes.
Assemble the pastes
Preheat oven to 375°F (190°C).
Roll dough to 1/8-inch thickness; cut 6-inch circles.
Spoon filling on one half, leaving a clean border.
Fold and crimp in the signature rope shape.
Brush with egg wash if using.
Transfer to a parchment-lined baking sheet.
Bake
Bake for 30–35 minutes, until golden brown.
Let cool slightly before devouring.