I was underweight.....well i still am slightly ( 182cm 70kg). Anyways I was around 58+ before. What I did was :

Breakfast:

Oats in Milk
Milk ( 300ml ) [ the oats milk is around 100ml, i take 300ml after the oats)
Eggs (2)

Lunch
Rice + Veggies ( Broccoli usually, and other greens) + Fish ( Macarel, Tuna or Sardins)
Milk (350ml)
Fruits ( Orange or Guava)
2 Slices of cheese + 2 slices of bread

Tea Time
Iko Biscuits 3-4 packets
2 Whole Meal bread + Peanut Butter
Tea ( green tea)

Dinner
Chicken Rice ( Without the skin....i hate the skin honestly)
Egg(1)- taken with the chicken rice
Milk (350ml)

Supper
2 Slices of Whole Meal Bread + 2 Slices of Cheese
4 Iko Biscuit Packets
Appeton Weight Gain ( Its around RM 60-90, you can get em from your local pharmacies)

I plan on continuing this till i reach my desired weight ( 78kg)
You could try it too if you'd like