Potato and Cheese Empanadas

Name: Potato and Cheese Empanadas
Ingredients: 3 Cups Cup4Cup flour; 2 Tablespoons granulated sugar; 1 Teaspoon salt; 1 Cup butter, cubed and cold; 1 large egg; 1/2 Cup cold buttermilk; 1 large russet potato; 2 Tablespoons canola oil; 1 medium yellow onion, small dice; 1 Teaspoon fresh garlic, minced; 1/4 Cup sour cream; 1 Cup shredded cheese (we like Cheddar); 1/4 Teaspoon cayenne; 1 Teaspoon parsley, chopped; Salt and pepper, to taste