1. Prep ingredients
Thinly slice the onion. Peel the potatoes and cut into 3cm chunks. Crumble the stock cubes into a heatproof jug, add the barbecue seasoning and 410ml (1⅔ cups) boiling water and stir to dissolve.
2. Make mash
Put the potato in a medium saucepan of cold salted water and bring to the boil (see Did you know?). Reduce the heat to medium and simmer for 12 mins or until tender. Drain, then return to the pan. Mash the potato until smooth. Add 15g butter, season with salt and pepper and stir to combine. Cover to keep warm.
3. Start stew
Meanwhile, heat 15g butter in a medium deep frypan over medium-high heat. Cook the sausages, turning regularly, for 4-5 mins until browned all over. Remove from the pan. Add the onion to the pan, reduce the heat to medium-low and cook, stirring occasionally, for 9-10 mins until soft and golden.
4. Simmer stew
Add 1 tbs tomato sauce and 1½ tbs plain flour to the onion and cook, stirring, for 1 min. Gradually add the stock, stirring constantly, and bring to a simmer. Add the sausages and cook for 3-4 mins until the sausages are cooked through and the sauce is thickened. Stir in 2 tsp dijon mustard, then remove from the heat. Taste, then season with salt and pepper.
5. Serve up
While the stew is cooking, bring a small saucepan of salted water to the boil. Add the peas and cook for 2 mins or until tender. Drain the peas. Divide the mash, sausage stew and peas among plates. Drizzle with tomato sauce and enjoy!
6. Did you know?
Why do we add potatoes to a pan of cold water? It's so they cook evenly. If they're added to boiling water, they become mushy and overdone on the outside by the time the inside is cooked through.