Vegetable Samosas with Potatoes and Peas

Name: Vegetable Samosas with Potatoes and Peas
Ingredients: 1 1/2 pounds russet potatoes, peeled and diced; 1/2 cup frozen peas; 1 teaspoon garam masala; 1 teaspoon salt; 1/2 teaspoon ground turmeric; 1/8 teaspoon cayenne pepper; Dough:; 1 1/2 cups all-purpose flour; 3/4 teaspoon salt; 1 tablespoon vegetable oil; 6 tablespoons ice water, or more if needed; Filling:; 1/4 cup butter; 1 tablespoon olive oil, or as needed; 1/2 cup chopped yellow onion; 4 teaspoons ginger-garlic paste; 1 squeeze lemon juice; 1 cup vegetable oil for frying, or as needed