Peel the potato and sweet potato and cut into chunks. Put in a medium saucepan of cold salted water and bring to the boil. Reduce the heat to medium and cook for 10-12 mins until tender. Drain, return to the pan and cover to keep warm. Bring a small saucepan of water to the boil for the peas.
Step 2 — Prep ingredients
While the potato is cooking, finely chop the onion and carrot. Crush or finely chop the garlic. Crumble 1 stock cube* into a heatproof jug, add 250ml (1 cup) boiling water and 1 tsp dijon mustard and stir to dissolve. Cut the chicken into 2cm chunks.
Step 3 — Cook vegetables
Heat 2 tsp olive oil and 20g butter in a medium deep frypan over medium-high heat. Cook the onion, carrot and garlic, stirring occasionally, for 4-5 mins until softened. Add the peas to the pan of boiling water and cook for 2 mins or until tender. Drain.
Step 4 — Cook chicken
Scatter 1 tbs flour over the vegetables and cook, stirring, for 2 mins or until foaming. Gradually add the stock, stirring constantly to prevent lumps forming, and bring to the boil. Add the chicken, reduce the heat to medium-low and cook, at a very gentle simmer, for 3 mins or until the chicken is cooked through and the sauce is thickened. Remove the pan from the heat.
Step 5 — Mash potato
Meanwhile, preheat the grill to medium-high. Mash the potato until smooth, season with salt and pepper and stir to combine.
Step 6 — Grill pie
Stir the peas into the chicken mixture, then transfer to a 1L (4 cup) baking dish. Spoon the mashed potato over the chicken mixture and scatter with the cheese. Grill for 5 mins or until melted and golden. Serve the pie at the table.