Bring an enormous dish of salted water to the bubble. Put the leeks, broccoli and celery in a huge steamer. Add the potatoes to the water and cook for 20 mins, with the vegetables steaming on top, until all are delicate. Channel the potatoes, at that point pound with a lot of flavoring, 25g of the margarine and all the yogurt.
While the veg cooks, empty the milk into a skillet, include the flour, the two mustards and remaining spread, and cook over a medium warmth, whisking constantly, until smooth and thickened. Blend down the middle the cheddar and season. Expel from warmth.
Gap the steamed veg and peas between 8 singular pie dishes. Pour over the sauce and top with the crush, at that point sprinkle over the rest of the cheddar.
Gather into cooler packs and use inside 3 months. To serve, unwrap and put the dishes on a preparing plate in the harsh elements stove, at that point set to 200C/180C fan/gas 6. Prepare for 50-55 mins until percolating and hot completely through.