Trim the thick central stalk on each leaf so the leaf lies flat without cutting through the blade. Stack the leaves from largest to smallest and keep them covered with a damp cloth.
Make the Besan Paste
Mix the besan, rice flour, ginger-green chilli paste, garlic, turmeric, coriander, cumin, red chilli powder, asafoetida, and salt in a bowl.
Add the jaggery and tamarind. Whisk in water gradually until the paste is lump-free and spreads like soft butter. Rest for 5 minutes, then add 1 teaspoon water if it stiffens.
Spread and Roll
Place the largest leaf veined side up and spread a thin layer of paste edge to edge. Stack 4-5 pasted leaves with smaller leaves on top.
Roll tightly from the stem end into a firm log and seal the seam with paste. Repeat if needed.
Steam
Grease the steamer plate and place the roll seam side down. Steam on medium-high for 18-22 minutes. The center should feel firm rather than pasty, and a skewer inserted through the thickest part should come out clean.
Rest in the covered steamer for 5 minutes, then cool until warm before slicing.
Temper or Pan-Fry
Cut the roll into 1-1.5 cm slices. For soft patra, prepare the mustard, sesame, curry leaf, chilli, and asafoetida tempering and pour it over the slices.
For crispy patra, reserve 1 tablespoon oil and pan-fry the slices for 2-3 minutes per side before adding the tempering.
Garnish with coconut and coriander. Serve warm or at room temperature.
Notes
Use young, tender colocasia leaves. Do not taste the leaves raw, and cook the rolls thoroughly.The batter should spread like soft butter. Thick batter can crack, while thin batter can slide off the leaves.Cool the steamed log until warm before slicing so the spirals stay neat.Steam the log up to 2 days ahead and refrigerate it airtight. Re-steam for 3-4 minutes before serving.Besan and rice flour are naturally gluten-free, but packaged asafoetida may contain wheat flour. Use hing labeled gluten-free and verify packaged spices if needed.