Clear space for big bowls of mash-topped comfort. We're piling in those cockle-warming flavours with rich lamb and lovely lentils, then stirring through some greens and letting it simmer down to cottage-style pie goodness. Those shepherds really knew what they were on about. Leftovers are a most welcome by-product of this one.
Peel and cut potatoes into 3cm pieces. Place in a saucepan and cover with cold, salted water. Bring to the boil and cook for 12–15 minutes or until tender. Drain well. Return potatoes to the saucepan with milk and butter and mash until smooth. Season well with salt and pepper. While potatoes are cooking, continue with step 2.
Boil kettle. Peel and finely dice onion. Finely chop carrot and celery. Pick thyme leaves from their stems. Rinse and drain lentils. Dissolve stock cube in 180ml (3⁄4 cup) boiling water.
Preheat overhead grill to high. Heat oil in frypan over medium-high heat. Add mince and cook, breaking up any lumps with the back of a wooden spoon, for 5–6 minutes or until golden. Add onion, carrot, celery, thyme, salt and pepper and cook, stirring, for 4–5 minutes or until softened.
Add tomato paste to pan and cook, stirring, for 30 seconds or until lightly caramelised. Add stock and lentils and bring to a rapid simmer. Reduce heat to medium and cook for 4–5 minutes or until fragrant and thickened. Stir through baby spinach leaves until wilted. Transfer filling to a roasting dish or pie dish.
Spoon mash over pie filling. Place on a baking tray (to catch any spills) and place under the preheated grill for 6–8 minutes or until the top is lightly golden brown.
Remove pie from oven and stand for a few minutes before dividing between bowls to serve.