High calorie foods?

I was seriously ill for about 2 months and lost a lot of weight (I was already thin to begin with) and am now trying to put the weight back on slowly and healthfully. Are their any foods that are higher-calorie that would be good for this? Any suggestions for dishes/recipes/etc that pack a good caloric punch? I’m healthy and my doctor says my body is in good shape now, but I’d like to gain back some of the weight since I’m pretty underweight now for my height. Any suggestions for foods that aren’t completely unhealthy and have a lot of calories?