Roasting besan on high heat, not stirring continuously, will burn the mixture making your besan turn bitter, and laddos will turn raw from the inside. Roast the besan always at medium to low flame till you get a nutty aroma. Taste test once you have finished roasting the besan. If you still feel it's raw, you will have to continue roasting for a few more minutes. The time it takes to roast besan will vary based on the thickness of the pan, the intensity of the flame, etc.