The easiest is to melt it very gently with some milk or cream and make it into a sauce which can be used for ice creams or pancakes or just poured over a cake.
Melting it with maida and cooling it will not taste good. The maida will taste raw.
Rewa, I do not have recipes of the Marwari Achars.
About the mangoes that are good for pickle:
Around Bombay the pickle is made before the rains. the vegetable seller himself is a good guide to tell you which mangoes.
I have been in Delhi for so long now, that I know in Delhi Ram Kela is the preferred mango for pickle. And this is available just as the rains start.
I do not know what recipe you follow. But I have noticed that some advise to add the oil after a few days. That certainly makes them tender faster, but also makes them mushy. Add the oil the same day and they stay alright. Of course the mangoes have to be firm and raw and white inside. If they are beginning to yellow means they are ripe and not good for pickle.
Buttermilk is what is called Chhaas.. When yogurt/dahi is churned a lot, the fat separates into little lumps. Remove them and the left over liquid is butter milk.
