If you plan to finish the dish in the oven, set it to heat to 180°C (350°F).
Boil 250 g potato, unpeeled, in a pot of water for roughly 20 minutes until completely tender. Once cool enough to handle, slip off the skins and thoroughly mash the flesh.
Slice a lengthwise sliver off the top of the 750 g marrow. Hollow out the seeds and pulp with a spoon, leaving a sturdy 1 cm border around the shell. Roughly chop the scooped-out flesh.
Make the filling: warm 26.4 g ghee in a skillet over medium heat. Sauté 200 g onion, chopped, for 2 to 3 minutes until softened. Stir in the chopped marrow flesh and fry for 3 to 5 minutes. Pull the pan from the heat, then work in the mashed potato, 24 g ginger, peeled and finely chopped, 12–18 g green chilli, 2 g coriander leaf, and salt to taste. Pack this mixture firmly into the hollowed marrow.
Prepare the gravy: melt 52.8 g ghee in a wide saucepan over medium flame. Sauté 250 g onion, grated, for 4 to 5 minutes until deep gold. Blend in 30 g garlic, ground, 10 g fresh ginger, ground, the ground spices for the sauce, and 5.8 g salt. Cook for 5 minutes, adding splashes of water whenever the spices threaten to stick.
Stir in 500 g tomato, chopped, and cook down for 5 to 7 minutes until the liquid reduces to a thick paste. Stir in 125 ml water and simmer gently for another 5 to 7 minutes.
To cook on the stovetop, place the stuffed marrow directly into the simmering sauce, secure the lid, and cook over medium heat for 20 to 30 minutes until tender. Alternatively, transfer the marrow to a greased baking tray, ladle the sauce around the sides, and bake for 30 minutes.
Scatter chopped coriander leaf over the top to garnish before serving.
Use the same weight; peel, deseed and cut into similar pieces. It is firmer and slightly more watery, so add a little less water and cook 5 minutes longer.
Use 120% of the weight; melt gently over low heat to avoid burning the milk solids, which will yield a softer, creamier richness rather than a nutty aroma.
Use 80% of the weight, finely shredded and browned slowly with a pinch of asafoetida. Replicates the bulk and natural sweetness in gravies without allium.
Use 15% to 20% of the weight (about 1 g for every 5 to 6 g fresh cloves). Whisk into sauces; gives a savoury, toasted garlic flavour without raw pungency.
Use 20% to 25% of the weight (1 g for every 4 to 5 g fresh). Stir into the gravy; adds peppery heat and warmth, though it misses the crisp, zesty kick of raw root.
Steep a tiny pinch (0.1 g per 2 g turmeric) in 2 tbsp warm water; use to match the rich golden hue. Contributes an aristocratic, honeyed floral flavour rather than earthy bitterness.
Use 40% to 50% of the fresh tomato weight mixed with a splash of water. Imparts a deeper red colour, thicker sauce, and slightly sweeter cooked flavour.