I don't know if you would love to try it. But it is from my personal experience to share with you. If you add one boiled potato two tiimes in your diet , you would definitely gain weight. It is easily available in your kitchen also.
I had a friend in my college days and he used to eat one boiled potato every day with his lunch. And within 4 months he gain weight quickly.
Nowadays I used to provide boil potato to my 6 years old boys diet. And he is also showing positive response.
We in India make many popular dishes with potato and one of the most popular one is
Aloo paratha(spiced potato stuffed flat bread). It is made by stuffing in a whole wheat flour dough and roasted on a pan till crisp golden.
You can make it and try in your breakfast.