There are many recipes. What I give here is my favourite version which I have not changed over the years.
With seasame seeds( ellu or til seeds )
Red chillies 1 cup
Udad dhal 1 cup
Ellu 1 cup
Salt
In a kadai heat ½ tsp oil & fry red chillies till crisp.
Remove & in the same kadai fry dhal to a light brown colour.
Remove & finally roast the ellu till it splutters.
Cool all the roasted ingredients well.
Powder in a mixi with salt.
A marble size jaggery is optional.
With gram dhal:
Red chillies 1 cup
Gram dhal 1 cup (1/2 cup gram dhal + ½ cup seasame seeds is also an option)
Udad dhal 1 cup
Salt
Method is the same as above.
If ellu is added , hing can be omitted , otherwise add I tsp hing powder also , roasted lightly before powdering.
In both the above recipes, if you like it very hot increase chillies to 1 ¼ cups.