Samosas Fried Potato Filled Pastries

Name: Samosas (Fried Potato-Filled Pastries)
Ingredients: 3 cups flour; 8 tbsp. unsalted butter, cubed and chilled; Kosher salt, to taste; 3⁄4 cup ice-cold water; 1⁄2 lb. russet potatoes, peeled and roughly chopped; 2 carrots, roughly chopped; 2 tbsp. canola oil, plus more; 1 tsp. cumin seeds; 1 small yellow onion, minced; 3⁄4 cup frozen peas, defrosted; 1⁄4 cup minced cilantro; 1⁄4 cup minced mint; 1⁄2 tsp. garam masala; 2 small green Thai chiles or 1 serrano, minced; 1 (1″) piece of ginger, peeled and minced; Tamarind and coconut-cilantro chutneys, for serving (optional)