• Heat your Instant Pot on sauté mode. Once it's hot, add vegetable oil, followed by onion and garlic. Sauté for a minute or two, then add the ground beef. Cook until the beef is browned and the onions are translucent.
  1 tablespoon vegetable oil, 1 small onion, 1 tablespoon minced garlic, 1 pound ground beef
  
• Remove and drain the beef, then return it to the Instant Pot. Add the frozen mixed vegetables, Worcestershire sauce, salt, and pepper. Mix well and sauté until the vegetables thaw and cook through.
  1 bag frozen mixed vegetables, 2 tablespoons Worcestershire sauce, pinch salt, pinch pepper
  
• While the vegetables are cooking, add melted butter, flour, and beef broth to a bowl. Mix well.
  2 tablespoons salted butter, 2 tablespoons flour, ½ cup beef broth
  
• Pour the mixture over the beef and veggies and stir to combine. Once it begins to thicken, transfer the contents of your pressure cooker to a casserole dish.
  
• Clean the inside of your Instant Pot and add water to it, along with peeled and cut russet potatoes. Add salt to the water and potatoes and cook on high pressure for 8 minutes. Carefully quick-release the pressure when 8 minutes are up.
  3 medium russet potatoes
  
• Drain the water from the pot, then place the potatoes back inside. Using a hand mixer, mash the potatoes until smooth. Add butter and milk and beat through before adding salt and pepper.
  1 teaspoon salt, ½ stick salted butter, 1½ cups whole milk, 1 teaspoon pepper
  
• Transfer your mashed potatoes to the casserole dish, spreading over top of the beef and vegetable mixture.
  
• Sprinkle with shredded cheddar cheese, then place it under your oven broiler for 5 minutes, or until golden brown. Serve and enjoy!
  1½ cups shredded cheddar cheese
  

Stovetop Instructions

Mashed Potato Topping

• Note: You can start making the potatoes just before preparing the beef filling so they finish at roughly the same time. I recommend starting the potatoes first. They will take about 45 minutes to make on the stove, while the filling takes roughly 15-20 minutes, so time yourself accordingly.
• Bring a large pot of water to a boil. Add 5 Tablespoons salt, then bring it back to a boil.
• Add diced potatoes to the water and boil for 20 to 25 minutes or until fork-tender.
  3 medium russet potatoes
• Drain the water from the pot. Using a hand mixer on low, whip the potatoes well until crumbly.
• Add butter to the pot with the potatoes, then continue mixing well until the butter fully combines with the potatoes and the potatoes are creamy.
  ½ stick salted butter
• Slowly add milk, salt, and pepper, while continuing to mix.
  1 teaspoon pepper, 1½ cups whole milk, 1 teaspoon salt

Shepherd's Pie Filling

• Heat a large skillet over medium-high heat on the stove. Once hot, add vegetable oil, along with onion and garlic. Saute 1-2 minutes.
  1 tablespoon vegetable oil, 1 small onion, 1 tablespoon minced garlic
• Add ground beef. Cook until the beef is browned and the onions are translucent. Break the beef apart as it cooks.
  1 pound ground beef
• Remove the beef mixture from the skillet, and drain. After draining, return it to the skillet.
• Mix in the frozen vegetables, Worcestershire sauce, salt, and pepper. Mix well and saute until the vegetables thaw and cook through.
  1 bag frozen mixed vegetables, 2 tablespoons Worcestershire sauce, pinch salt, pinch pepper
• While the vegetables are cooking, add melted butter, flour, and beef broth to a bowl, and mix well.
  2 tablespoons salted butter, 2 tablespoons flour, ½ cup beef broth
• Pour the mixture over the beef and veggies, and stir to combine. Once it begins to thicken, transfer the contents of the skillet to a casserole dish and spread it out evenly.

Assembling and Broiling

• Once mixed and creamy, spread the mashed potatoes over top of the beef and vegetable mixture in the casserole dish.
• Sprinkle with shredded cheddar cheese, then place under the oven broiler for 5 minutes, or until golden brown and bubbly.