Matilde's Beef Empanadas (Las Empanadas de Carne de Matilde)

Ingredients

• 2 medium white onions, peeled and chopped
• ½ lb. finely chopped beef chuck
• 2 tbsp. salted butter
• 2 tbsp. corn oil
• 1½ tsp. pella (rendered beef fat)
• 1½ tsp. dried oregano
• 1½ tsp. sugar
• 1½ tsp. all-purpose flour
• 1 tsp. ground black pepper
• ½-¾ tsp. red pepper flakes
• 30 pitted brined green or black olives, drained
• 4 hard-cooked eggs, peeled and each cut into 8 wedges
• 2 tbsp. salt
• 5¼ cups cake flour
• 1 cup self-rising flour
• 1¼ cups cornstarch
• 4½ tsp. powdered milk
• 1 tsp. baking powder
• ¼ cup pella (rendered beef fat)
• 9 tbsp. salted butter
• 2 eggs, beaten with ½ tsp. water