Here's a super-simple recipe that Keith and I really enjoy. It is from Real Simple a couple years ago and I've made it a number of times.
Easy Shepherd's Pie
1 pound ground beef
1/3 c. ketchup
1 tsp. Worcestershire sauce
8 oz. frozen mixed vegetables (such as carrots, peas, and corn), thawed
1/4 c. shredded Cheddar (optional)
1 16-oz. package refrigerated or frozen and thawed mashed potatoes
Heat oven to 400 degrees. Place the beef in a large skillet and cook over medium-high heat until no trace of pink remains, about 5 minutes. Spoon off and discard any fat. Stir in the ketchup and Worcestershire. Add the vegetables and cook, stirring, for 1 minute. Spoon the beef mixture into a baking dish. Mix the cheese (if using) with the potatoes in a medium bowl. Spread the potatoes over the beef and bake until heated through, 10 minutes. Divide among individual plates.
So that's the basic recipe. I departed a little bit from it. First, I used ground turkey.
Then I used way more vegetables than the recipe calls for. We had peas and corn frozen, so I thawed them out and then realized I had some carrots and celery in the fridge that needed to be used up, so I went ahead and threw them in too.
Then I made my own mashed potatoes because, well, it's cheaper than buying a tub of the refrigerated kind. And I'm cheap.
So the point is the recipe is really easy to adapt and cooking is more fun when it's a bit of an adventure. And Keith agrees. Most of the time.