Thanks for the query.
Firstly understand that weight gain is very dependent on genetics and metabolism along with your daily diet and exercise routine.
It is important to know that just
eating just two heavy meals a day will not help.
Weight gain is all about taking more calories than you burn. Eating the right foods at the right time is very important. There is no one food that helps weight gain.
Eat meals at frequent intervals. You need to eat at least 6 main and mid meals a day.
Eat a mid meal between each main meal.
Avoid junk foods.
Include dairy, eggs, nuts, fruits, dry fruits, starchy vegetables, rice, bread, whole grain
cereals, smoothies, masala milk, ghee, cream in your meals.
Just eating sugary, sweet foods is not good. Try to have healthy deserts like kheer, chikki or lassi.
Exercise at least thrice a week. It helps development of muscle mass and improves appetite.
Even if you were to take just medicines or supplements they will not work in isolation. You need to have a calorie and nutrient dense meal and good exercise routine, it's crucial.