In a food processor, pulse the flour and salt to combine. Add the cubed cold butter and pulse 3-4 times to break up into smaller chunks. With the food processor running, add the cold coconut milk or water and continue to process until mixture thickens and starts to come together but is still crumbly. This should take about 10 seconds.

Dump the dough out onto a clean surface and gather into a ball. Cut in half and shape each half into a disk. Wrap in plastic wrap and chill for 2 hours. Dough can be stored in the fridge for up to 5 days or double wrapped in the freezer for up to 2 months.

Add 2 tablespoons of the butter to a large skillet placed over medium heat. Season the cubed chicken with salt and pepper and add it to the skillet. Do not overcrowd the pan, cook in batches if needed. Cook until edges turn golden brown, about 5 minutes. Turn and cook for an additional 2 minutes. Remove from pan and set aside.

Place remaining 1 tablespoon butter in the skillet. Add the onions and cook until softened, about 5 minutes. Add the garlic and cook for 1 minute more. Stir in the tomato paste, curry powder, and flour. Add the coconut milk very gradually while whisking constantly. Add the chicken stock. Cook, stirring frequently, until thickened, about 7-10 minutes.

Add the cooked chicken, potatoes, and carrots and cook until vegetables are slightly tender, about 5 minutes. Stir in the peas and cilantro, and add additional salt and pepper to taste. Remove from heat to let cool slightly while you prepare the crust.

Roll out the second disk of dough into a large circle. Cut into strips for a lattice or keep intact. Pour the filling into the bottom crust and top with lattice or circle of crush. Trim edges of crust to 1 inch overhang, pinch together and tuck into pie dish.

Brush with egg wash and cut vents in the top crust if not using lattice. Bake until crust is golden and filling is bubbly, 45-60 minutes. If crust browns too quickly, cover with foil for the remainder of baking time.