Fill a large pan with water and add a pinch of salt. Scrub and peel the potatoes and chop them into bite-sized pieces. Slide the potatoes into the pan and bring to the boil. Simmer for 15-20 mins, till the potatoes are soft enough to be crushed with a fork.

Meanwhile, fill and boil your kettle. Use kitchen scissors to snip the sun dried tomatoes into a heatproof jug and pour in 200ml boiling water. Set aside to soak for 10-15 mins.

While the sun dried tomatoes soak, trim, peel and finely chop the onion. Trim and finely chop the carrots (no need to peel them). Trim the dry ends off the celery and finely slice it. Warm 1 tbsp olive oil in a medium pan on a medium heat. Add the onion, carrots and celery and fry for 5 mins, stirring a few times, till the veg start to brown.

Meanwhile, tear the portobello mushrooms into small pieces. Peel and grate or crush the garlic. Stir the mushrooms and garlic into the veg. Season with salt and pepper and fry, stirring, for 5 mins.

Drop the thyme sprigs into the pan. Drain and rinse the lentils, and add them, along with the tomato sauce. Pour in the sun dried tomatoes and their stock. Bring to the boil, then turn the heat down and cover. Simmer for 15 mins, stirring once or twice, till the sauce thickens a little.

The potatoes should be tender by now. Drain them, then tip them back into the pan. Add 1 tbsp olive oil and a pinch of salt and pepper. Mash the potatoes till smooth.

Set your grill to medium-high. Fish the thyme sprigs out of the pan and taste the sauce. Add a pinch more salt or pepper if you think it needs it. If your frying pan can go under the grill, then leave the lentil mix in there. Otherwise, spoon the mushroom and lentil pie filling into a heatproof dish. Top the filling with the mash.

Slide the pan or dish under the grill and cook for 6-8 mins, till bubbling and golden. Cool for a few mins before serving.