Stir-Fried Mashed Potato with Preserved Mustard Greens

Name: Stir-Fried Mashed Potato with Preserved Mustard Greens (Suan Cai Chao Tu Dou Ni 酸菜炒土豆泥)
Cuisine: Chinese
Ingredients: 2 tbsp finely sliced spring onion greens; 60 g Sichuanese ya cai or ‘snow vegetable’; 3 tbsp cooking oil or lard; 350 g leftover cooked potatoes; Ground white pepper; Salt