Batata Merhiya Recipe from Algeria with Potatoes, Ground Beef, and Gruyère

Ingredients

• 1 lb (454 g) potatoes , peeled, cooked, and mashed
• 2 tbsp butter
• 1 tsp salt
• 2 tsp olive oil
• 1 small onion , finely chopped
• 0.5 lb (227 g) ground beef
• 0.25 tsp pepper
• 1 medium egg , beaten
• 2 oz (57 g) gruyère cheese , grated