Preheat oven to 350F

Cook Potatoes: Cut potatoes in one-inch slices ( if small, just in half) and place in a large pot. Cover with one-inch salted water. Bring to a boil, lower heat, cover and simmer until very tender about 20-25 minutes.

Cook lentils: Set lentils to cook in salted water (unless cooked already – and you could absolutely do this ahead) about 20-25 minutes (see notes) simmer until tender, but not falling apart, al dente.

Make the filling: In a large 10-12 inch ovenproof skillet (or wide, shallow dutch oven) -heat the ghee over medium high heat and saute the onion 2-3 minutes, lower heat to med, add garlic, saute 2 mintues, add carrots, celery, cook 5-7 mintues. Add salt, cumin, coriander, fenugreek leaves and garam masala.

Add broth. Bring to a simmer, cover and simmer on med low, until carrots are cooked through about 7-8 minutes.

While this is simmering, MAKE THE GRAVY: Over medium heat, in a little pot, simmer the whole seeds ( cumin seeds and fennel seeds)  in ghee or oil until fragrant and golden. Add flour, whisking, stirring and toasting the flour one minute. Gradually whisk in the warm veggie broth. Cook until slightly thickened. Add this gravy to the filling, along with the peas and drained lentils. Mix to combine.

Taste the filling and adjust salt and pepper. Add more garam masala if you like. The filling should have  thick stew-like, saucy consistency. If too dry, add a splash of broth or water. If too watery, simmer off some of that liquid. If the filling is too watery, the mashed potatoes will sink.

Mash the potatoes: Drain the potatoes (saving some hot potato water) return to the same pot and mash with the 3-4 tablespoons ghee and yogurt. If potatoes seem dry or too stiff, add a little warm potato water to loosen. If you want extra richness a little milk, nut milk, half and half, or whipping cream is nice. I add about ½ cup. (Adding more yogurt will make these too tangy.) Season with salt, pepper and curry powder. Mash and whip until relatively smooth and light and fluffy. Taste and adjust salt.

ASSEMBLE: Place 8 big dollops over the lentils stew and fill in the spaces with smaller spoonfuls, carefully spreading out, maybe making a pattern with the back of the spoon, like frosting a cake.

Place in the oven until golden and bubbling, about 20-25 minutes. Feel free to brown the top under a broiler.

Garnish with scallions, chives or cilantro.