Method
1. Add butter, all purpose flour and scallion to a clean saucepan
2. Gradually add milk and stir until light golden - approx 1 min, medium heat
3. Cook until thickened and turn off heat - approx 4 min
4. Add dijon mustard, peas, fresh chives and mixed fresh fish
5. Transfer fish pie filling to ceramic baking dish
6. Add potato and fluff with a fork
7. Sprinkle with cheddar cheese
8. Bake until golden brown - 30 min, 200°C / 395°F