Comfort food is a traditional food that is usually easily prepared, and provides feelings of nostalgia to the person who had been socialized in the culture of its origin. Comfort food is more "feel good" food than healthy food. This is the food to turn to when you feel blue, or are sick.
I'll restrict my examples to the Gulf Coastal South, the South as I know best.
Grits -- While they can be prepared in a variety of ways, including cheesy grits, I prefer the traditional butter and salt seasoning. Hash browns at breakfast is a vile experience. Some bacon or link sausage complements it nicely.
Jambalaya -- A traditional Cajun dish based on rice, some onion and possibly sweet pepper or celery seasoning, and whatever meat is available for adding: andouille, ham, shrimp, chicken, duck. Maybe not alligator.
Red Beans and Rice -- A traditional washday Monday meal. The red beans are even better as leftovers! Use some ham pieces and flavor with a hambone. Season with Tabasco sauce.
Gumbo -- A dish made of meat or shellfish, a roux, seasoning vegetables, and either okra or filé.
Barbecue pork or beef -- Get this from a barbecue joint, either as take-out or eat on the premises. I prefer pulled pork or beef, as opposed to chopped. A variety of sauces is fine, but no mayonnaise-based sauces, please! Establishments that serve barbecue are referred to as "joints"; this does not imply a negative judgment about them.
Banana pudding -- The recipe is so easy. Line the bottom of the bowl with vanilla wafers, cut up some ripe bananas, and pour some vanilla pudding mixed with the bananas on the wafers. Let cool in the refrigerator.
Moon Pie -- This is Southern junk food. Best with a Co-Cola or a RC. That sinful, feel-good result is known as a Moon Pie High.
Pecan pie -- Here's a good recipe from The Food Network:
Hush puppies -- Another term for corn fritter. Actually, corn muffins are good too. Serve these with seafood, barbecue, or good ole Texas chili.
My Two Landmarks
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