Place a heavy bottomed pan over a medium flame, add the freshly grated coconut and jaggery, cook, with frequent stirring, till the jaggery is well incorporated into the coconut. 7-10 minutes I would reckon. Now gently pour the milk, continue to cook till the milk has almost dried up.
Allow to cool to room temperature. Keep aside.
For the Jaggery Syrup
Heat the water and jaggery in a pot for about 15-20 minutes till you get a nice golden syrup.
For the Outer Coating
Boil the sweet potatoes till soft. Peel, mash well.
Add rice flour and plain flour to the mashed sweet potatoes, knead well to make a smooth dough, taking care that there are no lumps.
If it is too soft, feel free to add some more plain flour. Add in small increments, too much flour shall make the coating too hard.
Assembling the Ranga Alur Pulis
Now take a dough ball on your palm, press it gently in the middle using your thumb forming a small oval cup. Place a small portion of the coconut mixture in the middle of the cup. (As shown in the picture)
Very gently bring the edges of the dough cup together to cover the stuffing and give it a oblong shape. As in the picture. Repeat for the rest of the dough.
Heat oil in a deep bottomed pan. Fry till golden. Keep aside on a kitchen absorbent towel.
Soak the fried pulis in the warm jaggery syrup, 20-30 minutes or so. Remove from syrup. Serve.